DNA and mRNA encoding an α4 subunit of human neuronal nicotinic acetylcholine receptor and cells transformed with same

ABSTRACT

DNA encoding human neuronal nicotinic acetylcholine receptor alpha and beta subunits, mammalian and amphibian cells containing said DNA, methods for producing alpha and beta subunits and recombinant (i.e., isolated or substantially pure) alpha subunits (specifically α 4  and α 7 ) and beta subunits (specifically β 4 ) are provided. In addition, combinations of subunits (i.e., α 1 , α 2 , α 3 , α 4 , and/or α 7  subunits in combination with β 4  subunits; or β 2 , β 3  and/or β 4  subunits in combination with α 4  and/or α 7  subunits) are provided.

The application is a divisional of U.S. application Ser. No. 08/028,031, filed Mar. 8, 1993, now abandoned.

This invention relates to DNA encoding human neuronal nicotinic acetylcholine receptor protein subunits, as well as the proteins themselves. In particular, human neuronal nicotinic acetylcholine receptor α-subunit-encoding DNA, α-subunit proteins, β-subunit-encoding DNA, β-subunit proteins, and combinations thereof are provided.

BACKGROUND OF THE INVENTION

Ligand-gated ion channels provide a means for communication between cells of the central nervous system. These channels convert a signal (e.g., a chemical referred to as a neurotransmitter) that is released by one cell into an electrical signal that propagates along a target cell membrane. A variety of neurotransmitters and neurotransmitter receptors exist in the central and peripheral nervous systems. Five families of ligand-gated receptors, including the nicotinic acetylcholine receptors (NAChRs) of neuromuscular and neuronal origins, have been identified (Stroud et al. (1990) Biochemistry 29:11009-11023). There is, however, little understanding of the manner in which the variety of receptors generates different responses to neurotransmitters or to other modulating ligands in different regions of the nervous system.

The nicotinic acetylcholine receptors (NAChRs) are multisubunit proteins of neuromuscular and neuronal origins. These receptors form ligand-gated ion channels that mediate synaptic transmission between nerve and muscle and between neurons upon interaction with the neurotransmitter acetylcholine (ACh). Since various nicotinic acetylcholine receptor (NAChR) subunits exist, a variety of NAChR compositions (i.e., combinations of subunits) exist. The different NAChR compositions exhibit different specificities for various ligands and are thereby pharmacologically distinguishable. Thus, the nicotinic acetylcholine receptors expressed at the vertebrate neuromuscular junction in vertebrate sympathetic ganglia and in the vertebrate central nervous system have been distinguished on the basis of the effects of various ligands that bind to different NAChR compositions. For example, the elapid α-neurotoxins that block activation of nicotinic acetylcholine receptors at the neuromuscular junction do not block activation of some neuronal nicotinic acetylcholine receptors that are expressed on several different neuron-derived cell lines.

Muscle NAChR is a glycoprotein composed of five subunits with the stoichiometry α₂ α(γ or ε)δ. Each of the subunits has a mass of about 50-60 kilodaltons (kd) and is encoded by a different gene. The α₂ β(γ or ε)δ complex forms functional receptors containing two ligand binding sites and a ligand-gated transmembrane channel. Upon interaction with a cholinergic agonist, muscle nicotinic AChRs conduct sodium ions. The influx of sodium ions rapidly short-circuits the normal ionic gradient maintained across the plasma membrane, thereby depolarizing the membrane. By reducing the potential difference across the membrane, a chemical signal is transduced into an electrical signal that signals muscle contraction at the neuromuscular junction.

Functional muscle nicotinic acetylcholine receptors have been formed with αβδγ subunits, αβγ subunits, αβδ subunits, αβγ subunits or αδ subunits, but not with only one subunit (see e.g., Kurosaki et al. (1987) FEBS Lett. 214: 253-258; Camacho et al. (1993) J. Neuroscience 13:605-613). In contrast, functional neuronal AChRs (nAChRs) can be formed from α subunits alone or combinations of α and β subunits. The larger α subunit is generally believed to be the ACh-binding subunit and the lower molecular weight β subunit is generally believed to be the structural subunit, although it has not been definitively demonstrated that the β subunit does not have the ability to bind ACh. Each of the subunits which participate in the formation of a functional ion channel are, to the extent they contribute to the structure of the resulting channel, "structural" subunits, regardless of their ability (or inability) to bind ACh. Neuronal AChRs (nAChRs), which are also ligand-gated ion channels, are expressed in ganglia of the autonomic nervous system and in the central nervous system (where they mediate signal transmission), in post-synaptic locations (where they modulate transmission), and in pre- and extra-synaptic locations (where they may have additional functions).

DNA encoding NAChRs has been isolated from several sources. Based on the information available from such work, it has been evident for some time that NAChRs expressed in muscle, in autonomic ganglia, and in the central nervous system are functionally diverse. This functional diversity could be due, at least in part, to the large number of different NAChR subunits which exist. There is an incomplete understanding, however, of how (and which) NAChR subunits combine to generate unique NAChR subtypes, particularly in neuronal cells. Indeed, there is evidence that only certain NAChR subtypes may be involved in diseases such as Alzheimer's disease. Moreover, it is not clear whether NAChRs from analogous tissues or cell types are similar across species.

Accordingly, there is a need for the isolation and characterization of DNAs encoding each human neuronal NAChR subunit, recombinant cells containing such subunits and receptors prepared therefrom. In order to study the function of human neuronal AChRs and to obtain disease-specific pharmacologically active agents, there is also a need to obtain isolated (preferably purified) human neuronal nicotinic AChRs, and isolated (preferably purified) human neuronal nicotinic AChR subunits. In addition, there is also a need to develop assays to identify such pharmacologically active agents.

The availability of such DNAs, cells, receptor subunits and receptor compositions will eliminate the uncertainty of speculating as to human nNAChR structure and function based on predictions drawn from non-human nNAChR data, or human or non-human muscle or ganglia NAChR data.

Therefore, it is an object herein to isolate and characterize DNA encoding subunits of human neuronal nicotinic acetylcholine receptors. It is also an object herein to provide methods for recombinant production of human neuronal nicotinic acetylcholine receptor subunits. It is also an object herein to provide purified receptor subunits and to provide methods for screening compounds to identify compounds that modulate the activity of human neuronal AChRs.

These and other objects will become apparent to those of skill in the art upon further study of the specification and claims.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the present invention, there are provided isolated DNAs encoding novel human alpha and beta subunits of neuronal NAChRs. In particular, isolated DNA encoding human α₄, α₇, and β₄ subunits of neuronal NAChRs are provided. Messenger RNA and polypeptides encoded by the above-described DNA are also provided.

Further in accordance with the present invention, there are provided recombinant human neuronal nicotinic AChR subunits, including α₄, α₇, and β₄ subunits, as well as methods for the production thereof. In addition, recombinant human neuronal nicotinic acetylcholine receptors containing at least one human neuronal nicotinic AChR subunit are also provided, as well as methods for the production thereof. Further provided are recombinant neuronal nicotinic AChRs that contain a mixture of one or more NAChR subunits encoded by a host cell, and one or more nNAChR subunits encoded by heterologous DNA or RNA (i.e., DNA or RNA as described herein that has been introduced into the host cell), as well as methods for the production thereof.

Plasmids containing DNA encoding the above-described subunits are also provided. Recombinant cells containing the above-described DNA, mRNA or plasmids are also provided herein. Such cells are useful, for example, for replicating DNA, for producing human NAChR subunits and recombinant receptors, and for producing cells that express receptors containing one or more human subunits.

Also provided in accordance with the present invention are methods for identifying cells that express functional nicotinic acetylcholine receptors. Methods for identifying compounds which modulate the activity of NAChRs are also provided.

The DNA, mRNA, vectors, receptor subunits, receptor subunit combinations and cells provided herein permit production of selected neuronal nicotinic AChR receptor subtypes and specific combinations thereof, as well as antibodies to said receptor subunits. This provides a means to prepare synthetic or recombinant receptors and receptor subunits that are substantially free of contamination from many other receptor proteins whose presence can interfere with analysis of a single NAChR subtype. The availability of desired receptor subtypes makes it possible to observe the effect of a drug substance on a particular receptor subtype and to thereby perform initial in vitro screening of the drug substance in a test system that is specific for humans and specific for a human neuronal nicotinic AChR subtype.

The availability of subunit-specific antibodies makes possible the application of the technique of immunohistochemistry to monitor the distribution and expression density of various subunits (e.g., in normal vs diseased brain tissue). Such antibodies could also be employed for diagnostic and therapeutic applications.

The ability to screen drug substances in vitro to determine the effect of the drug on specific receptor compositions should permit the development and screening of receptor subtype-specific or disease-specific drugs. Also, testing of single receptor subunits or specific receptor subtype combinations with a variety of potential agonists or antagonists provides additional information with respect to the function and activity of the individual subunits and should lead to the identification and design of compounds that are capable of very specific interaction with one or more of the receptor subunits or receptor subtypes. The resulting drugs should exhibit fewer unwanted side effects than drugs identified by screening with cells that express a variety of subtypes.

Further in relation to drug development and therapeutic treatment of various disease states, the availability of DNAs encoding human nNAChR subunits enables identification of any alterations in such genes (e.g., mutations) which may correlate with the occurrence of certain disease states. In addition, the creation of animal models of such disease states becomes possible, by specifically introducing such mutations into synthetic DNA sequences which can then be introduced into laboratory animals or in vitro assay systems to determine the effects thereof.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 presents a restriction map of two pCMV promoter-based vectors, pCMV-T7-2 and pCMV-T7-3.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, we have isolated and characterized DNAs encoding novel human alpha and beta subunits of neuronal NAChRs. Specifically, isolated DNAs encoding human α₄, α₇, and β₄ subunits of neuronal NAChRs are described herein. Recombinant messenger RNA (mRNA) and recombinant polypeptides encoded by the above-described DNA are also provided.

As used herein, isolated (or substantially pure) as a modifier of DNA, RNA, polypeptides or proteins means that the DNA, RNA, polypeptides or proteins so designated have been separated from their in vivo cellular environments through the efforts of human beings. Thus as used herein, isolated (or substantially pure) DNA refers to DNAs purified according to standard techniques employed by those skilled in the art (see, e.g., Maniatis et al.(1982) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.).

Similarly, as used herein, "recombinant" as a modifier of DNA, RNA, polypeptides or proteins means that the DNA, RNA, polypeptides or proteins so designated have been prepared by the efforts of human beings, e.g., by cloning, recombinant expression, and the like. Thus as used herein, recombinant proteins, for example, refers to proteins produced by a recombinant host, expressing DNAs which have been added to that host through the efforts of human beings.

As used herein, a human alpha subunit gene is a gene that encodes an alpha subunit of a human neuronal nicotinic acetylcholine receptor. The alpha subunit is a subunit of the NAChR to which ACh binds. Assignment of the name "alpha" to a putative nNAChR subunit, according to Deneris et al. [Tips (1991) 12:34-40] is based on the conservation of adjacent cysteine residues in the presumed extracellular domain of the subunit that are the homologues of cysteines 192 and 193 of the Torpedo alpha subunit (see Noda et al. (1982) Nature 299:793-797). As used herein, an alpha subunit subtype refers to a human nNAChR subunit that is encoded by DNA that hybridizes under high stringency conditions to at least one of the nNAChR alpha subunit-encoding DNAs (or deposited clones) disclosed herein. An alpha subunit also binds to ACh under physiological conditions and at physiological concentrations and, in the optional presence of a beta subunit (i.e., some alpha subunits are functional alone, while others require the presence of a beta subunit), generally forms a functional AChR as assessed by methods described herein or known to those of skill in this art.

Also contemplated are alpha subunits encoded by DNAs that encode alpha subunits as defined above, but that by virtue of degeneracy of the genetic code do not necessarily hybridize to the disclosed DNA or deposited clones under specified hybridization conditions. Such subunits also form a functional receptor, as assessed by the methods described herein or known to those of skill in the art, generally with one or more beta subunit subtypes. Typically, unless an alpha subunit is encoded by RNA that arises from alternative splicing (i.e., a splice variant), alpha-encoding DNA and the alpha subunit encoded thereby share substantial sequence homology with at least one of the alpha subunit DNAs (and proteins encoded thereby) described or deposited herein. It is understood that DNA or RNA encoding a splice variant may overall share less than 90% homology with the DNA or RNA provided herein, but include regions of nearly 100% homology to a DNA fragment or deposited clone described herein, and encode an open reading frame that includes start and stop codons and encodes a functional alpha subunit.

As used herein, a splice variant refers to variant NAChR subunit-encoding nucleic acid(s) produced by differential processing of primary transcript(s) of genomic DNA, resulting in the production of more than one type of mRNA. cDNA derived from differentially processed genomic DNA will encode NAChR subunits that have regions of complete amino acid identity and regions having different amino acid sequences. Thus, the same genomic sequence can lead to the production of multiple, related mRNAs and proteins. Both the resulting mRNAs and proteins are referred to herein as "splice variants".

Stringency of hybridization is used herein to refer to conditions under which polynucleic acid hybrids are stable. As known to those of skill in the art, the stability of hybrids is reflected in the melting temperature (T_(m)) of the hybrids. T_(m) can be approximated by the formula:

    81.5° C.-16.6(log.sub.10 [Na.sup.+ ])+0.41(%G+C)-600/l,

where l is the length of the hybrids in nucleotides. T_(m) decreases approximately 1-1.5° C. with every 1% decrease in sequence homology. In general, the stability of a hybrid is a function of sodium ion concentration and temperature. Typically, the hybridization reaction is performed under conditions of lower stringency, followed by washes of varying, but higher, stringency. Reference to hybridization stringency relates to such washing conditions. Thus, as used herein:

(1) HIGH STRINGENCY refers to conditions that permit hybridization of only those nucleic acid sequences that form stable hybrids in 0.01M NaCl at 65° C. (i.e., if a hybrid is not stable in 0.018M NaCl at 65° C., it will not be stable under high stringency conditions, as contemplated herein). High stringency conditions can be provided, for example, by hybridization in 50% formamide, 5× Denhardt's solution, 5× SSPE, 0.2% SDS at 42° C., followed by washing in 0.1× SSPE, and 0.1% SDS at 65° C.;

(2) MODERATE STRINGENCY refers to conditions equivalent to hybridization in 50% formamide, 5× Denhardt's solution, 5× SSPE, 0.2% SDS at 42° C., followed by washing in 0.2× SSPE, 0.2% SDS, at 65° C.; and

(3) LOW STRINGENCY refers to conditions equivalent to hybridization in 10% formamide, 5× Denhardt's solution, 6× SSPE, 0.2% SDS, followed by washing in 1× SSPE, 0.2% SDS, at 50° C.

It is understood that these conditions may be duplicated using a variety of buffers and temperatures and that they are not necessarily precise.

Denhardt's solution and SSPE (see, e.g., Sambrook, Fritsch, and Maniatis, in: Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory Press, 1989) are well known to those of skill in the art as are other suitable hybridization buffers. For example, SSPE is pH 7.4 phosphate-buffered 0.18M NaCl. SSPE can be prepared, for example, as a 20× stock solution by dissolving 175.3 g of NaCl, 27.6 g of NaH₂ PO₄ and 7.4 g EDTA in 800 ml of water, adjusting the pH to 7.4, and then adding water to 1 liter. Denhardt's solution (see, Denhardt (1966) Biochem. Biophys. Res. Commun. 23:641) can be prepared, for example, as a 50× stock solution by mixing 5 g Ficoll (Type 400, Pharmacia LKB Biotechnology, INC., Piscataway N.J.), 5 g of polyvinylpyrrolidone, 5 g bovine serum albumin (Fraction V; Sigma, St. Louis Mo.) water to 500 ml and filtering to remove particulate matter.

The phrase "substantial sequence homology" is used herein in reference to the nucleotide sequence of DNA, the ribonucleotide sequence of RNA, or the amino acid sequence of protein, that have slight and non-consequential sequence variations from the actual sequences disclosed herein. Species having substantial sequence homology are considered to be equivalent to the disclosed sequences and as such are within the scope of the appended claims. In this regard, "slight and non-consequential sequence variations" mean that "homologous" sequences, i.e., sequences that have substantial homology with the DNA, RNA, or proteins disclosed and claimed herein, are functionally equivalent to the sequences disclosed and claimed herein. Functionally equivalent sequences will function in substantially the same manner to produce substantially the same compositions as the nucleic acid and amino acid compositions disclosed and claimed herein. In particular, functionally equivalent DNAs encode proteins that are the same as those disclosed herein or that have conservative amino acid variations, such as substitution of a non-polar residue for another non-polar residue or a charged residue for a similarly charged residue. These changes include those recognized by those of skill in the art as those that do not substantially alter the tertiary structure of the protein.

In practice, the term substantially the same sequence means that DNA or RNA encoding two proteins hybridize under conditions of high stringency and encode proteins that have the same sequence of amino acids or have changes in sequence that do not alter their structure or function. As used herein, substantially identical sequences of nucleotides share at least about 90% identity, and substantially identical amino acid sequences share more than 95% amino acid identity. It is recognized, however, that proteins (and DNA or mRNA encoding such proteins) containing less than the above-described level of homology arising as splice variants or that are modified by conservative amino acid substitutions (or substitution of degenerate codons) are contemplated to be within the scope of the present invention.

As used herein, "α₄ subunit DNA" refers to DNA encoding a neuronal nicotinic acetylcholine receptor subunit of the same name. Such DNA can be characterized in a number of ways, for example

said DNA may encode the amino acid sequence set forth in SEQ. ID No. 6, or

said DNA may encode the amino acid sequence encoded by clone HnAChRα4.2, deposited under ATCC Accession No. 69239, or

the 5' nucleotides of said DNA may encode the amino acid sequence encoded by clone HnAChRα4.1, deposited under ATCC Accession No. 69152.

Presently preferred α₄ -encoding DNAs can be characterized as follows

said DNA may hybridize to the coding sequence set forth in SEQ. ID No. 5 (preferably to substantially the entire coding sequence thereof, i.e., nucleotides 184-2067) under high stringency conditions, or

said DNA may hybridize under high stringency conditions to the sequence (preferably to substantially the entire sequence) of the α₄ -encoding insert of clone HnAChRα4.2, deposited under ATCC Accession No. 69239, or

the 5' nucleotides of said DNA may hybridize under high stringency conditions to the sequence of the α₄ -encoding insert of clone HnAChRα4.1, deposited under ATCC Accession No. 69152.

Especially preferred α₄ -encoding DNAs of the invention are characterized as follows

DNA having substantially the same nucleotide sequence as the coding region set forth in SEQ. ID No. 5 (i.e., nucleotides 184-2067 thereof), or

DNA having substantially the same nucleotide sequence as the α₄ -encoding insert of clone HnAChRα4.2, deposited under ATCC Accession No. 69239, or

the 5' nucleotides of said DNA have substantially the same sequence as the α₄ -encoding insert of clone HnAChRα4.1, deposited under ATCC Accession No. 69152.

Typically, unless an α₄ subunit arises as a splice variant, α₄ -encoding DNA will share substantial sequence homology (i.e., greater than about 90%), with the α₄ DNAs described or deposited herein. DNA or RNA encoding a splice variant may share less than 90% overall sequence homology with the DNA or RNA provided herein, but such a splice variant would include regions of nearly 100% homology to the above-described DNAS.

As used herein, "α₇, subunit DNA" refers to DNA encoding a neuronal nicotinic acetylcholine receptor subunit of the same name. Such DNA can be characterized in a number of ways, for example, the nucleotides of said DNA may encode the amino acid sequence set forth in SEQ. ID No. 8. Presently preferred α₇ -encoding DNAs can be characterized as DNA which hybridizes under high stringency conditions to the coding sequence set forth in SEQ. ID No. 7 (preferably to substantially the entire coding sequence thereof, i.e., nucleotides 73-1581). Especially preferred α₇ -encoding DNAs of the invention are characterized as having substantially the same nucleotide sequence as the coding sequence set forth in SEQ. ID No. 7 (i.e., nucleotides 73-1581 thereof).

Typically, unless an α₇ subunit arises as a splice variant, α₇ -encoding DNA will share substantial sequence homology (greater than about 90%) with the α₇ DNAs described or deposited herein. DNA or RNA encoding a splice variant may share less than 90% overall sequence homology with the DNA or RNA provided herein, but such DNA would include regions of nearly 100% homology to the above-described DNA.

The α₇ subunits derived from the above-described DNA are expected to bind to the neurotoxin α-bungarotoxin (α-bgtx). The activity of AChRs that contain α₇ subunits should be inhibited upon interaction with α-bgtx. Amino acid residues 210 through 217, as set forth in SEQ ID No. 8, are believed to be important elements in the binding of α-bgtx (see, for example, Chargeux et al. Trends Pharmacol. Sci. (1992) 13:299-301).

As used herein, a human beta subunit gene is a gene that encodes a beta subunit of a human neuronal nicotinic acetylcholine receptor. Assignment of the name "beta" to a putative nNAChR subunit, according to Deneris et al. supra, is based on the lack of adjacent cysteine residues (which are characteristic of alpha subunits). The beta subunit is frequently referred to as the structural NAChR subunit (although it is possible that beta subunits also have ACh binding properties). Combination of beta subunit(s) with appropriate alpha subunit(s) leads to the formation of a functional receptor. As used herein, a beta subunit subtype refers to a nNAChR subunit that is encoded by DNA that hybridizes under high stringency conditions to at least one of the nNAChR-encoding DNAs (or deposited clones) disclosed herein. A beta subunit forms a functional NAChR, as assessed by methods described herein or known to those of skill in this art, with appropriate alpha subunit subtype(s).

Also contemplated are beta subunits encoded by DNAs that encode beta subunits as defined above, but that by virtue of degeneracy of the genetic code do not necessarily hybridize to the disclosed DNA or deposited clones under the specified hybridization conditions. Such subunits also form functional receptors, as assessed by the methods described herein or known to those of skill in the art, in combination with appropriate alpha subunit subtype(s). Typically, unless a beta subunit is encoded by RNA that arises as a splice variant, beta-encoding DNA and the beta subunit encoded thereby share substantial sequence homology with the beta-encoding DNA and beta subunit protein described herein. It is understood that DNA or RNA encoding a splice variant may share less than 90% overall homology with the DNA or RNA provided herein, but such DNA will include regions of nearly 100% homology to the DNA described herein.

As used herein, "β₄ subunit DNA" refers to DNA encoding a neuronal nicotinic acetylcholine receptor subunit of the same name. Such DNA can be characterized in a number of ways, for example, the nucleotides of said DNA may encode the amino acid sequence set forth in SEQ. ID No. 12. Presently preferred β₄ -encoding DNAs can be characterized as DNA which hybridizes under high stringency conditions to the coding sequence set forth in SEQ. ID No. 11 (preferably to substantially the entire coding sequence thereof, i.e., nucleotides 87-1583). Especially preferred β₄ -encoding DNAs of the invention are characterized as having substantially the same nucleotide sequence as set forth in SEQ. ID No. 11.

Typically, unless a β₄ subunit arises as a splice variant, α₄ -encoding DNA will share substantial sequence homology (greater than about 90%) with the β₄ DNAs described or deposited herein. DNA or RNA encoding a splice variant may share less than 90% overall sequence homology with the DNA or RNA provided herein, but such DNA would include regions of nearly 100% homology to the above-described DNA.

DNA encoding human neuronal nicotinic AChR alpha and beta subunits may be isolated by screening suitable human cDNA or human genomic libraries under suitable hybridization conditions with DNA disclosed herein (including nucleotides derived from any of SEQ ID Nos. 5, 7, 9 or 11, or with any of the deposited clones referred to herein (e.g., ATCC accession no. 69239 or 69152). Suitable libraries can be prepared from neuronal tissue samples, hippocampus tissue, or cell lines, such as the human neuroblastoma cell line IMR32 (ATCC Accession No. CCL127), and the like. The library is preferably screened with a portion of DNA including the entire subunit-encoding sequence thereof, or the library may be screened with a suitable probe.

As used herein, a probe is single-stranded DNA or RNA that has a sequence of nucleotides that includes at least 14 contiguous bases that are the same as (or the complement of) any 14 bases set forth in any of SEQ ID Nos. 1, 3, 5, 7, 9, or 11, or in the subunit encoding DNA in any of the deposited clones described herein (e.g., ATCC accession no. 69239 or 69152). Preferred regions from which to construct probes include 5' and/or 3' coding sequences, sequences predicted to encode transmembrane domains, sequences predicted to encode the cytoplasmic loop, signal sequences, acetylcholine (ACh) and α-bungarotoxin (α-bgtx) binding sites, and the like. Amino acids 210-220 are typically involved in ACh and α-bgtx binding. The approximate amino acid residues which comprise such regions for other preferred probes are set forth in the following table:

    __________________________________________________________________________     Subunit                                                                            Signal Sequence                                                                        TMD1*                                                                               TMD2 TMD3 TMD4 Cytoplasmic Loop                               __________________________________________________________________________     α.sub.2                                                                      1-55    264-289                                                                             297-320                                                                             326-350                                                                             444-515                                                                             351-443                                          α.sub.3 1-30 240-265 273-296 302-326 459-480 327-458                     α.sub.4 1-33 241-269 275-289 303-330 593-618 594-617                     α.sub.7 1-23 229-256 262-284 290-317 462-487 318-461                     β.sub.2 1-25 234-259 267-288 295-320 453-477 321-452                      β.sub.4 1-23 234-258 264-285 290-319 454-478 320-453                    __________________________________________________________________________      *TMD = transmembrane domain                                              

Alternatively, portions of the DNA can be used as primers to amplify selected fragments in a particular library.

After screening the library, positive clones are identified by detecting a hybridization signal; the identified clones are characterized by restriction enzyme mapping and/or DNA sequence analysis, and then examined, by comparison with the sequences set forth herein or with the deposited clones described herein, to ascertain whether they include DNA encoding a complete alpha or beta subunit. If the selected clones are incomplete, they may be used to rescreen the same or a different library to obtain overlapping clones. If desired, the library can be rescreened with positive clones until overlapping clones that encode an entire alpha or beta subunit are obtained. If the library is a cDNA library, then the overlapping clones will include an open reading frame. If the library is genomic, then the overlapping clones may include exons and introns. In both instances, complete clones may be identified by comparison with the DNA and encoded proteins provided herein.

Complementary DNA clones encoding various subtypes of human nNAChR alpha and beta subunits have been isolated. Each subtype of the subunit appears to be encoded by a different gene. The DNA clones provided herein may be used to isolate genomic clones encoding each subtype and to isolate any splice variants by screening libraries prepared from different neural tissues. Nucleic acid amplification techniques, which are well known in the art, can be used to locate splice variants of human NAChR subunits. This is accomplished by employing oligonucleotides based on DNA sequences surrounding divergent sequence(s) as primers for amplifying human RNA or genomic DNA. Size and sequence determinations of the amplification products can reveal the existence of splice variants. Furthermore, isolation of human genomic DNA sequences by hybridization can yield DNA containing multiple exons, separated by introns, that correspond to different splice variants of transcripts encoding human NAChR subunits.

It has been found that not all subunit subtypes are expressed in all neural tissues or in all portions of the brain. Thus, in order to isolate cDNA encoding particular subunit subtypes or splice variants of such subtypes, it is preferable to screen libraries prepared from different neuronal or neural tissues. Preferred libraries for obtaining DNA encoding each subunit include: hippocampus to isolate human α₄ - and α₅ -encoding DNA; IMR32 to isolate human α₃ -, α₅ -, α₇ - and β₄ -encoding DNA, thalamus to isolate α₂ and β₂ -encoding DNA; and the like.

It appears that the distribution of expression of human neuronal nicotinic AChRs differs from the distribution of such receptors in rat. For example, RNA encoding the rat α₄ subunit is abundant in rat thalamus, but is not abundant in rat hippocampus (see, e.g., Wada et al. (1989) J. Comp. Neurol 284:314-335). No α₄ -encoding clones could be obtained, however, from a human thalamus library. Instead, human α₄ clones were ultimately obtained from a human hippocampus library. Thus, the distribution of α₄ nNAChR subunit in humans and rats appears to be quite different.

Rat α₃ subunit appears to be a CNS-associated subunit that is abundantly expressed in the thalamus and weakly expressed in the brain stem (see, e.g., Boulter et al. (1986) Nature 319:368-374; Boulter et al. (1987) Proc. Natl. Acad. Sci. USA 84:7763-7767; and Wada et al. (1989) J. Comp. Neurol 284:314-335). In efforts to clone DNA encoding the human nicotinic AChR α₃ subunit, however, several human libraries, including a thalamus library, were unsuccessfully screened. Surprisingly, clones encoding human α₃ subunit were ultimately obtained from a brain stem library and from IMR32 cells that reportedly express few, if any, functional nicotinic acetylcholine receptors (see, e.g., Gotti et al. ((1986) Biochem. Biophys. Res. Commun. 137: 1141-1147, and Clementi et al. (1986) J. Neurochem. 47: 291-297).

Rat α₇ subunit transcript reportedly is abundantly expressed in the hippocampus (see Seguela et al. (1993) J. Neurosci. 13:596-604). Efforts to clone DNA encoding a human α₇ subunit from a human hippocampus library (1×10⁶ recombinants) were unsuccessful. Surprisingly, clones encoding a human NAChR α₇ subunit were ultimately obtained from an IMR32 cell cDNA library.

The above-described nucleotide sequences can be incorporated into vectors for further manipulation. As used herein, vector (or plasmid) refers to discrete elements that are used to introduce heterologous DNA into cells for either expression or replication thereof. Selection and use of such vehicles are well within the level of skill of the art.

An expression vector includes vectors capable of expressing DNAs that are operatively linked with regulatory sequences, such as promoter regions, that are capable of effecting expression of such DNA fragments. Thus, an expression vector refers to a recombinant DNA or RNA construct, such as a plasmid, a phage, recombinant virus or other vector that, upon introduction into an appropriate host cell, results in expression of the cloned DNA. Appropriate expression vectors are well known to those of skill in the art and include those that are replicable in eukaryotic cells and/or prokaryotic cells and those that remain episomal or those which integrate into the host cell genome. Presently preferred plasmids for expression of invention AChR subunits in eukaryotic host cells, particularly mammalian cells, include cytomegalovirus (CMV) promoter-containing vectors such as pCMV, pcDNAl, and the like.

As used herein, a promoter region refers to a segment of DNA that controls transcription of DNA to which it is operatively linked. The promoter region includes specific sequences that are sufficient for RNA polymerase recognition, binding and transcription initiation. This portion of the promoter region is referred to as the promoter. In addition, the promoter region includes sequences that modulate this recognition, binding and transcription initiation activity of RNA polymerase. These sequences may be cis acting or may be responsive to trans acting factors. Promoters, depending upon the nature of the regulation, may be constitutive or regulated. Exemplary promoters contemplated for use in the practice of the present invention include the SV40 early promoter, the cytomegalovirus (CMV) promoter, the mouse mammary tumor virus (MMTV) steroid-inducible promoter, Moloney murine leukemia virus (MMLV) promoter, and the like.

As used herein, the term "operatively linked" refers to the functional relationship of DNA with regulatory and effector sequences of nucleotides, such as promoters, enhancers, transcriptional and translational stop sites, and other signal sequences. For example, operative linkage of DNA to a promoter refers to the physical and functional relationship between the DNA and the promoter such that the transcription of such DNA is initiated from the promoter by an RNA polymerase that specifically recognizes, binds to and transcribes the DNA. In order to optimize expression and/or in vitro transcription, it may be necessary to remove or alter 5' untranslated portions of the clones to remove extra, potential alternative translation initiation (i.e., start) codons or other sequences that interfere with or reduce expression, either at the level of transcription or translation. Alternatively, consensus ribosome binding sites (see, for example, Kozak (1991) J. Biol. Chem. 266:19867-19870) can be inserted immediately 5' of the start codon to enhance expression. The desirability of (or need for) such modification may be empirically determined.

As used herein, expression refers to the process by which polynucleic acids are transcribed into mRNA and translated into peptides, polypeptides, or proteins. If the polynucleic acid is derived from genomic DNA, expression may, if an appropriate eukaryotic host cell or organism is selected, include splicing of the mRNA.

Particularly preferred vectors for transfection of mammalian cells are the pSV2dhfr expression vectors, which contain the SV40 early promoter, mouse dhfr gene, SV40 polyadenylation and splice sites and sequences necessary for maintaining the vector in bacteria, cytomegalovirus (CMV) promoter-based vectors such as pCDNAl (Invitrogen, San Diego, Calif.), and MMTV promoter-based vectors such as pMSG (Catalog No. 27-4506-01 from Pharmacia, Piscataway, N.J.).

Full-length DNAs encoding human neuronal NAChR subunits have been inserted into vector pCMV-T7, a pUC19-based mammalian cell expression vector containing the CMV promoter/enhancer, SV40 splice/donor sites located immediately downstream of the promoter, a polylinker downstream of the splice/donor sites, followed by an SV40 polyadenylation signal. Placement of NAChR subunit DNA between the CMV promoter and SV40 polyadenylation signal provides for constitutive expression of the foreign DNA in a mammalian host cell transfected with the construct. For inducible expression of human NAChR subunit-encoding DNA in a mammalian cell, the DNA can be inserted into a plasmid such as pMSG. This plasmid contains the mouse mammary tumor virus (MMTV) promoter for steroid-inducible expression of operatively associated foreign DNA. If the host cell does not express endogenous glucocorticoid receptors required for uptake of glucocorticoids (i.e., inducers of the MMTV promoter) into the cell, it is necessary to additionally transfect the cell with DNA encoding the glucocorticoid receptor (ATCC accession no. 67200). Full-length human DNA clones encoding human α₃, α₄, α₇, β₂ and β₄ have also been subcloned into pIBI24 (International Biotechnologies, Inc., New Haven, Conn.) or pCMV-T7-2 for synthesis of in vitro transcripts.

In accordance with another embodiment of the present invention, there are provided cells containing the above-described polynucleic acids (i.e., DNA or mRNA). Such host cells as bacterial, yeast and mammalian cells can be used for replicating DNA and producing nAChR subunit(s). Methods for constructing expression vectors, preparing in vitro transcripts, transfecting DNA into mammalian cells, injecting oocytes, and performing electrophysiological and other analyses for assessing receptor expression and function as described herein are also described in PCT Application Nos. PCT/US91/02311, PCT/US91/05625 and PCT/US92/11090, and in co-pending U.S. application Ser. Nos. 07/504,455, 07/563,751 and 07/812,254. The subject matter of these applications are hereby incorporated by reference herein in their entirety.

Incorporation of cloned DNA into a suitable expression vector, transfection of eukaryotic cells with a plasmid vector or a combination of plasmid vectors, each encoding one or more distinct genes or with linear DNA, and selection of transfected cells are well known in the art (see, e.g., Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press). Heterologous DNA may be introduced into host cells by any method known to those of skill in the art, such as transfection with a vector encoding the heterologous DNA by CaPO₄ precipitation (see, e.g., Wigler et al. (1979) Proc. Natl. Acad. Sci. 76:1373-1376). Recombinant cells can then be cultured under conditions whereby the subunit(s) encoded by the DNA is (are) expressed. Preferred cells include mammalian cells (e.g., HEK 293, CHO and Ltk cells), yeast cells (e.g., methylotrophic yeast cells, such as Pichia pastoris), bacterial cells (e.g., Escherichia coli), and the like.

While the DNA provided herein may be expressed in any eukaryotic cell, including yeast cells (such as, for example, P. pastoris (see U.S. Pat. Nos. 4,882,279, 4,837,148, 4,929,555 and 4,855,231), Saccharomyces cerevisiae, Candida tropicalis, Hansenula polymorpha, and the like), mammalian expression systems, including commercially available systems and other such systems known to those of skill in the art, for expression of DNA encoding the human neuronal nicotinic AChR subunits provided herein are presently preferred. Xenopus oocytes are preferred for expression of RNA transcripts of the DNA.

In preferred embodiments, DNA is ligated into a vector, and introduced into suitable host cells to produce transformed cell lines that express a specific human nNAChR receptor subtype, or specific combinations of subtypes. The resulting cell lines can then be produced in quantity for reproducible quantitative analysis of the effects of drugs on receptor function. In other embodiments, mRNA may be produced by in vitro transcription of DNA encoding each subunit. This mRNA, either from a single subunit clone or from a combination of clones, can then be injected into Xenopus oocytes where the MRNA directs the synthesis of the human receptor subunits, which then form functional receptors. Alternatively, the subunit-encoding DNA can be directly injected into oocytes for expression of functional receptors. The transfected mammalian cells or injected oocytes may then be used in the methods of drug screening provided herein.

Cloned full-length DNA encoding any of the subunits of human neuronal nicotinic AChR may be introduced into a plasmid vector for expression in a eukaryotic cell. Such DNA may be genomic DNA or cDNA. Host cells may be transfected with one or a combination of plasmids, each of which encodes at least one human neuronal nicotinic AChR subunit.

Eukaryotic cells in which DNA or RNA may be introduced include any cells that are transfectable by such DNA or RNA or into which such DNA or RNA may be injected. Preferred cells are those that can be transiently or stably transfected and also express the DNA and RNA. Presently most preferred cells are those that can form recombinant or heterologous human neuronal nicotinic AChRs comprising one or more subunits encoded by the heterologous DNA. Such cells may be identified empirically or selected from among those known to be readily transfected or injected.

Exemplary cells for introducing DNA include cells of mammalian origin (e.g., COS cells, mouse L cells, Chinese hamster ovary (CHO) cells, human embryonic kidney cells, African green monkey cells and other such cells known to those of skill in the art), amphibian cells (e.g., Xenopus laevis oocytes), yeast cells (e.g., Saccharomyces cerevisiae, Pichia pastoris), and the like. Exemplary cells for expressing injected RNA transcripts include Xenopus laevis oocytes. Cells that are preferred for transfection of DNA are known to those of skill in the art or may be empirically identified, and include HEK 293 (which are available from ATCC under accession #CRL 1573); Ltk cells (which are available from ATCC under accession #CCL1.3); COS-7 cells (which are available from ATCC under accession #CRL 1651); and DG44 cells (dhfr CHO cells; see, e.g., Urlaub et al. (1986) Cell. Molec. Genet. 12: 555). Presently preferred cells include DG44 cells and HEK 293 cells, particularly HEK 293 cells that have been adapted for growth in suspension and that can be frozen in liquid nitrogen and then thawed and regrown. HEK 293 cells are described, for example, in U.S. Pat. No. 5,024,939 to Gorman (see, also, Stillman et al. (1985) Mol. Cell. Biol. 5:2051-2060).

DNA may be stably incorporated into cells or may be transiently introduced using methods known in the art. Stably transfected mammalian cells may be prepared by transfecting cells with an expression vector having a selectable marker gene (such as, for example, the gene for thymidine kinase, dihydrofolate reductase, neomycin resistance, and the like), and growing the transfected cells under conditions selective for cells expressing the marker gene. To produce such cells, the cells should be transfected with a sufficient concentration of subunit-encoding nucleic acids to form human neuronal nicotinic AChRs that contain the human subunits encoded by heterologous DNA. The precise amounts and ratios of DNA encoding the subunits may be empirically determined and optimized for a particular combination of subunits, cells and assay conditions. Recombinant cells that express neuronal nicotinic AChR containing subunits encoded only by the heterologous DNA or RNA are especially preferred.

Heterologous DNA may be maintained in the cell as an episomal element or may be integrated into chromosomal DNA of the cell. The resulting recombinant cells may then be cultured or subcultured (or passaged, in the case of mammalian cells) from such a culture or a subculture thereof. Methods for transfection, injection and culturing recombinant cells are known to the skilled artisan. Similarly, the human neuronal nicotinic AChR subunits may be purified using protein purification methods known to those of skill in the art. For example, antibodies or other ligands that specifically bind to one or more of the subunits may be used for affinity purification of the subunit or human neuronal nicotinic AChRs containing the subunits.

In accordance with one embodiment of the present invention, methods for producing cells that express human neuronal nicotinic AChR subunits and functional receptors are also provided. In one such method, host cells are transfected with DNA encoding at least one alpha subunit of a neuronal nicotinic acetylcholine receptor and at least one beta subunit of a neuronal nicotinic acetylcholine receptor. Using methods such as northern blot or slot blot analysis, transfected cells that contain alpha and/or beta subunit encoding DNA or RNA can be selected. Transfected cells are also analyzed to identify those that express NAChR protein. Analysis can be carried out, for example, by measuring the ability of cells to bind acetylcholine, nicotine, or a nicotine agonist, compared to the nicotine binding ability of untransfected host cells or other suitable control cells, by electrophysiologically monitoring the currents through the cell membrane in response to a nicotine agonist, and the like.

In particularly preferred aspects, eukaryotic cells which contain heterologous DNAs express such DNA and form recombinant functional neuronal nicotinic AChR(s). In more preferred aspects, recombinant neuronal nicotinic AChR activity is readily detectable because it is a type that is absent from the untransfected host cell or is of a magnitude not exhibited in the untransfected cell. Such cells that contain recombinant receptors could be prepared, for example, by causing cells transformed with DNA encoding the human neuronal nicotinic AChR α₃ and β₄ subunits to express the corresponding proteins. The resulting synthetic or recombinant receptor would contain only the α₃ and β₄ nNAChR subunits. Such a receptor would be useful for a variety of applications, e.g., as part of an assay system free of the interferences frequently present in prior art assay systems employing non-human receptors or human tissue preparations. Furthermore, testing of single receptor subunits with a variety of potential agonists or antagonists would provide additional information with respect to the function and activity of the individual subunits. Such information may lead to the identification of compounds which are capable of very specific interaction with one or more of the receptor subunits. Such specificity may prove of great value in medical application.

Thus, DNA encoding one or more human neuronal nicotinic AChR subunits may be introduced into suitable host cells (e.g., eukaryotic or prokaryotic cells) for expression of individual subunits and functional NAChRs. Preferably combinations of alpha and beta subunits may be introduced into cells: such combinations include combinations of any one or more of α₁, α₂, α₃, α₄, α₅ and α₇ with β₂ or β₄. Sequence information for α₁ is presented in Biochem. Soc. Trans. (1989) 17:219-220; sequence information for α₅ is presented in Proc. Natl. Acad. Sci. USA (1992) 89:1572-1576; and sequence information for α₂, α₃, α₄, α₇, β₂ and β₄ is presented in the Sequence Listing provided herewith. Presently preferred combinations of subunits include any one or more of α₁, α₂, α₃ or α₅ with β₄ ; or α₄ or α₇ in combination with either β₂ or β₄. It is recognized that some of the subunits may have ion transport function in the absence of additional subunits. For example, the α₇ subunit is functional in the absence of any added beta subunit.

As used herein, "α₂ subunit DNA" refers to DNA that encodes a human neuronal nicotinic acetylcholine receptor subunit of the same name, and to DNA that hybridizes under conditions of high stringency to the DNA of SEQ ID No. 1, or to the DNA of deposited clone having ATCC Accession No. 68277, or to DNA that encodes the amino acid sequence set forth in SEQ ID No. 2. Typically, unless an α₂ subunit arises as a splice variant, an α₂ DNA shares substantial sequence homology (greater than about 90%) with the α₂ DNA described herein. DNA or RNA encoding a splice variant may share less than 90% overall sequence homology with the DNA or RNA described herein, but such a splice variant would include regions of nearly 100% homology to the above-described DNA.

As used herein, "α₃ subunit DNA" refers to DNA that encodes a neuronal subunit of the same name, and to DNA that hybridizes under conditions of high stringency to the DNA of SEQ ID No. 3, or to the DNA of deposited clone having ATCC Accession No. 68278, or to DNA that encodes the amino acid sequence set forth in SEQ ID No. 4. Typically, unless an α₃ arises as a splice variant, an α₃ DNA shares substantial sequence homology (greater than about 90%) with the α₃ DNA described herein. DNA or RNA encoding a splice variant may share less than 90% overall sequence homology with the DNA or RNA provided herein, but such a splice variant would include regions of nearly 100% homology to the above described DNA.

As used herein, "α₅ subunit DNA" refers to DNA that encodes a human neuronal nicotinic acetylcholine receptor subunit of the same name, as described, for example, by Chini et al. (1992) Proc. Natl. Acad. Sci. USA 89:1572-1576.

As used herein, "β₂ subunit DNA" refers to DNA that encodes a neuronal subunit of the same name and, to DNA that hybridizes under conditions of high stringency to the DNA of SEQ ID No. 9, or to the DNA of deposited clone HnAChRβ2, having ATCC Accession No. 68279, or to DNA encoding the amino acid sequence set forth in SEQ ID No. 10. Typically, unless a β₂ subunit arises as a splice variant, a β₂ DNA shares substantial sequence homology (greater than about 90%) with the β₂ DNA described herein. DNA or RNA encoding a splice variant may share overall less than 90% homology with the DNA or RNA provided herein, but such a splice variant would include regions of nearly 100% homology to the above-described DNA.

In certain embodiments, eukaryotic cells with heterologous human neuronal nicotinic AChRs are produced by introducing into the cell a first composition, which contains at least one RNA transcript that is translated in the cell into a subunit of a human neuronal nicotinic AChR. In preferred embodiments, the subunits that are translated include an alpha subunit of a human neuronal nicotinic AChR. More preferably, the composition that is introduced contains an RNA transcript which encodes an alpha subunit and also contains an RNA transcript which encodes a beta subunit of a human neuronal nicotinic AChR. RNA transcripts can be obtained from cells transfected with DNAs encoding human neuronal nicotinic acetylcholine receptor subunits or by in vitro transcription of subunit-encoding DNAs. Methods for in vitro transcription of cloned DNA and injection of the resulting mRNA into eukaryotic cells are well known in the art. Amphibian oocytes are particularly preferred for expression of in vitro transcripts of the human nNAChR DNA clones provided herein. See, for example, Dascal (1989) CRC Crit. Rev. Biochem. 22:317-387, for a review of the use of Xenopus oocytes to study ion channels.

Thus, pairwise (or stepwise) introduction of DNA or RNA encoding alpha and beta subtypes into cells is possible. The resulting cells may be tested by the methods provided herein or known to those of skill in the art to detect functional AChR activity. Such testing will allow the identification of pairs of alpha and beta subunit subtypes that produce functional AChRs, as well as individual subunits that produce functional AChRs.

As used herein, activity of a human neuronal nicotinic AChR refers to any activity characteristic of an NAChR. Such activity can typically be measured by one or more in vitro methods, and frequently corresponds to an in vivo activity of a human neuronal nicotinic AChR. Such activity may be measured by any method known to those of skill in the art, such as, for example, measuring the amount of current which flows through the recombinant channel in response to a stimulus.

Methods to determine the presence and/or activity of human neuronal nicotinic AChRs include assays that measure nicotine binding, ⁸⁶ Rb ion-flux, Ca²⁺ influx, the electrophysiological response of cells, the electrophysiological response of oocytes transfected with RNA from the cells, and the like. In particular, methods are provided herein for the measurement or detection of an AChR-mediated response upon contact of cells containing the DNA or mRNA with a test compound.

As used herein, a recombinant or heterologous human neuronal nicotinic AChR refers to a receptor that contains one or more subunits encoded by heterologous DNA that has been introduced into and expressed in cells capable of expressing receptor protein. A recombinant human neuronal nicotinic AChR may also include subunits that are produced by DNA endogenous to the host cell. In certain embodiments, recombinant or heterologous human neuronal nicotinic AChR may contain only subunits that are encoded by heterologous DNA.

As used herein, heterologous or foreign DNA and RNA are used interchangeably and refer to DNA or RNA that does not occur naturally as part of the genome of the cell in which it is present or to DNA or RNA which is found in a location or locations in the genome that differ from that in which it occurs in nature. Typically, heterologous or foreign DNA and RNA refers to DNA or RNA that is not endogenous to the host cell and has been artificially introduced into the cell. Examples of heterologous DNA include DNA that encodes a human neuronal nicotinic AChR subunit, DNA that encodes RNA or proteins that mediate or alter expression of endogenous DNA by affecting transcription, translation, or other regulatable biochemical processes, and the like. The cell that expresses heterologous DNA may contain DNA encoding the same or different expression products. Heterologous DNA need not be expressed and may be integrated into the host cell genome or maintained episomally.

Recombinant receptors on recombinant eukaryotic cell surfaces may contain one or more subunits encoded by the DNA or mRNA encoding human neuronal nicotinic AChR subunits, or may contain a mixture of subunits encoded by the host cell and subunits encoded by heterologous DNA or mRNA. Recombinant receptors may be homogeneous or may be a mixture of subtypes. Mixtures of DNA or mRNA encoding receptors from various species, such as rats and humans, may also be introduced into the cells. Thus, a cell can be prepared that expresses recombinant receptors containing only α₃ and β₄ subunits, or any other combination of alpha and beta subunits provided herein. For example, α₄ and/or α₇ subunits of the present invention can be co-expressed with β₂ and/or β₄ receptor subunits; similarly, β₄ subunits according to the present invention can be co-expressed with α₂, α₃, α₄, α₅ and/or α₇ receptor subunits. As noted previously, some of the nNAChR subunits may be capable of forming functional receptors in the absence of other subunits, thus co-expression is not always required to produce functional receptors.

As used herein, a functional neuronal nicotinic AChR is a receptor that exhibits an activity of neuronal nicotinic AChRs as assessed by any in vitro or in vivo assay disclosed herein or known to those of skill in the art. Possession of any such activity that may be assessed by any method known to those of skill in the art and provided herein is sufficient to designate a receptor as functional. Methods for detecting NAChR protein and/or activity include, for example, assays that measure nicotine binding, ⁸⁶ Rb ion-flux, Ca²⁺ influx, the electrophysiological response of cells containing heterologous DNA or mRNA encoding one or more receptor subunit subtypes, and the like. Since all combinations of alpha and beta subunits may not form functional receptors, numerous combinations of alpha and beta subunits should be tested in order to fully characterize a particular subunit and cells which produce same. Thus, as used herein, "functional" with respect to a recombinant or heterologous human neuronal nicotinic AChR means that the receptor channel is able to provide for and regulate entry of human neuronal nicotinic AChR-permeable ions, such as, for example, Na⁺, K⁺, Ca²⁺ or Ba²⁺, in response to a stimulus and/or bind ligands with affinity for the receptor. Preferably such human neuronal nicotinic AChR activity is distinguishable, such as by electrophysiological, pharmacological and other means known to those of skill in the art, from any endogenous nicotinic AChR activity that may be produced by the host cell.

In accordance with a particular embodiment of the present invention, recombinant human neuronal nicotinic AChR-expressing mammalian cells or oocytes can be contacted with a test compound, and the modulating effect(s) thereof can then be evaluated by comparing the AChR-mediated response in the presence and absence of test compound, or by comparing the AChR-mediated response of test cells, or control cells (i.e., cells that do not express nNAChRs), to the presence of the compound.

As used herein, a compound or signal that "modulates the activity of a neuronal nicotinic AChR" refers to a compound or signal that alters the activity of NAChR so that activity of the NAChR is different in the presence of the compound or signal than in the absence of the compound or signal. In particular, such compounds or signals include agonists and antagonists. The term agonist refers to a substance or signal, such as ACh, that activates receptor function; and the term antagonist refers to a substance that interferes with receptor function. Typically, the effect of an antagonist is observed as a blocking of activation by an agonist. Antagonists include competitive and non-competitive antagonists. A competitive antagonist (or competitive blocker) interacts with or near the site specific for the agonist (e.g., ligand or neurotransmitter) for the same or closely situated site. A non-competitive antagonist or blocker inactivates the functioning of the receptor by interacting with a site other than the site that interacts with the agonist.

As understood by those of skill in the art, assay methods for identifying compounds that modulate human neuronal nicotinic AChR activity (e.g., agonists and antagonists) generally require comparison to a control. One type of a "control" cell or "control" culture is a cell or culture that is treated substantially the same as the cell or culture exposed to the test compound, except the control culture is not exposed to test compound. For example, in methods that use voltage clamp electrophysiological procedures, the same cell can be tested in the presence and absence of test compound, by merely changing the external solution bathing the cell. Another type of "control" cell or "control" culture may be a cell or a culture of cells which are identical to the transfected cells, except the cells employed for the control culture do not express functional human neuronal nicotinic AChRs. In this situation, the response of test cell to test compound is compared to the response (or lack of response) of receptor-negative (control) cell to test compound, when cells or cultures of each type of cell are exposed to substantially the same reaction conditions in the presence of compound being assayed.

The functional recombinant human neuronal nicotinic AChR includes at least an alpha subunit, or an alpha subunit and a beta subunit of a human neuronal nicotinic AChR. Eukaryotic cells expressing these subunits have been prepared by injection of RNA transcripts and by transfection of DNA. Such cells have exhibited nicotinic AChR activity attributable to human neuronal nicotinic AChRs that contain one or more of the heterologous human neuronal nicotinic AChR subunits. For example, Xenopus laevis oocytes that had been injected with in vitro transcripts of the DNA encoding human neuronal nicotinic AChR α₃ and β₄ subunits exhibited AChR agonist induced currents; whereas cells that had been injected with transcripts of either the α₃ or β₄ subunit alone did not. In addition, HEK 293 cells that had been co-transfected with DNA encoding human neuronal NAChR α₃ and β₄ subunits exhibited AChR agonist-induced increases in intracellular calcium concentration, whereas control HEK 293 cells (i.e., cells that had not been transfected with α₃ - and β₄ -encoding DNA) did not exhibit any AChR agonist-induced increases in intracellular calcium concentration.

With respect to measurement of the activity of functional heterologous human neuronal nicotinic AChRs, endogenous AChR activity and, if desired, activity of AChRs that contain a mixture of endogenous host cell subunits and heterologous subunits, should, if possible, be inhibited to a significant extent by chemical, pharmacological and electrophysiological means.

Deposits

The deposited clones have been deposited at the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Md., U.S.A. 20852, under the terms of the Budapest Treaty on the International Recognition of Deposits of Microorganisms for Purposes of Patent Procedure and the Regulations promulgated under this Treaty. Samples of the deposited material are and will be available to industrial property offices and other persons legally entitled to receive them under the terms of the Treaty and Regulations and otherwise in compliance with the patent laws and regulations of the United States of America and all other nations or international organizations in which this application, or an application claiming priority of this application, is filed or in which any patent granted on any such application is granted. In particular, upon issuance of a U.S. patent based on this or any application claiming priority to or incorporating this application by reference thereto, all restrictions upon availability of the deposited material will be irrevocably removed.

The invention will now be described in greater detail with reference to the following non-limiting examples.

EXAMPLE 1 Isolation of DNA Encoding Human nNAChR Subunits

A. DNA Encoding a Human nNAChR β₄ Subunit

Random primers were used in synthesizing cDNA from RNA isolated from the IMR32 human neuroblastoma cell line (the cells had been treated with dibutyryl cAMP and bromodeoxyuridine prior to constructing the library). The library constructed from the cDNAs was screened with a fragment of a rat nicotinic AChR β₄ subunit cDNA. Hybridization was performed at 42° C. in 5× SSPE, 5× Denhardt's solution, 50% formamide, 200 μg/ml herring sperm DNA and 0.2% SDS. Washes were performed in 0.1× SSPE, 0.2% SDS at 65° C. Five clones were identified that hybridized to the probe.

The five clones were plaque-purified and characterized by restriction enzyme mapping and DNA sequence analysis. The insert DNA of one of the five clones contained the complete coding sequence of a β₄ subunit of a human nicotinic AChR (see nucleotides 87-1583 of SEQ ID No. 11). The amino acid sequence deduced from the nucleotide sequence of the full-length clone has ˜81% identity with the amino acid sequence deduced from the rat nicotinic AChR β₄ subunit DNA. Several regions of the deduced rat and human β₄ amino acid sequences are notably dissimilar: amino acids 1-23 (the human sequence has only ˜36% identity with respect to the rat sequence), 352-416 (the human sequence has only ˜48% identity with respect to the rat sequence), and 417-492 (the human sequence has only ˜78% identity with respect to the rat sequence). Furthermore, amino acids 376-379 in the rat β₄ subunit are not contained in the human β₄ subunit.

B. DNA Encoding a Human nNAChR α₇ Subunit

An amplified IMR32 cell cDNA library (1×10⁶ recombinants; cells treated with dibutyryl cAMP and bromodeoxyuridine) was screened with a fragment of a rat nicotinic AChR α₇ subunit cDNA. The hybridization conditions were identical to those described above for screening an IMR32 cell cDNA library with the rat β₄ subunit DNA. Washes were performed in 0.2× SSPE, 0.2% SDS at 65° C. Seven positive clones were identified by hybridization to the labeled rat DNA probe. Six of the clones were plaque-purified and characterized by restriction enzyme mapping and DNA sequence analysis. one of the clones contains the complete coding sequence of a human AChR receptor α₇ subunit gene (see nucleotides 73-1581 of SEQ ID No. 7).

C. DNA Encoding a Human nNAChR α₄ Subunit

Random primers were used in synthesizing cDNA from RNA isolated from human hippocampus tissue. cDNAs larger than 2.0 kb were inserted into the λgt10 phage vector to create a cDNA library. Approximately 1×10⁶ recombinants were screened with a fragment of a DNA encoding a rat nicotinic AChR α₄ subunit using the same hybridization and washing conditions as described above for screening an IMR₃₂ cell CDNA library for α₇ subunit cDNAs. Three clones hybridized strongly to the probe. Two of these three clones, designated KEα4.1 and KEα4.2, have been deposited with the American Type Culture Collection (ATCC, Rockville, Md.) and assigned accession nos. 69152 and 69239, respectively.

Characterization of the plaque-purified clones revealed that one of the clones, KEα4.2, contains the complete coding sequence of a human nicotinic AChR α4 subunit gene (coding sequence of this human α₄ subunit cDNA is provided as nucleotides 184-2067 in SEQ ID No. 5). Comparison of the 5' ends of the coding sequences of the human and rat α4 subunit cDNAs reveals that the rat sequence contains an 18-nucleotide segment that is not present in the human sequence.

D. DNA Encoding Human nNAChR α₂, α₃, & β₂ Subunits

Plasmids containing DNA that encodes and/or that can be used to isolate DNA that encodes human neuronal nicotinic acetylcholine receptor α₂, α₃ and β₂ subunits have been deposited with the American Type Culture Collection (ATCC). The clone names and deposit accession numbers are:

    ______________________________________                                         Subunit    Clone Name                                                                               ATCC Accession No.                                        ______________________________________                                         α.sub.2                                                                             HnAChRα2                                                                           68277                                                       α.sub.3 HnACHRα3 68278                                             β.sub.2 HnAChRβ2 68279                                             ______________________________________                                    

In addition, DNA sequences that encode full-length α₂, α₃ and β₂ subunits are set forth in SEQ ID Nos. 1, 3 and 9, respectively.

EXAMPLE 2 Preparation of Constructs for the Expression of Recombinant Human Neuronal Nicotinic AChR Subunits

Isolated cDNAs encoding human neuronal nicotinic AChR subunits were incorporated into vectors for use in expressing the subunits in mammalian host cells and for use in generating in vitro transcripts of the DNAs to be expressed in Xenopus oocytes. Several different vectors were utilized in preparing the constructs as follows.

A. Construct for Expression of a Human nNAChR α₃ Subunit

DNA encoding a human neuronal nicotinic AChR α₃ subunit was subcloned into the pCMV-T7-2 general expression vector to create pCMV-KEα3. Plasmid pCMV-T7-2 (see FIG. 1) is a pUC19-based vector that contains a CMV promoter/enhancer, SV40 splice donor/splice acceptor sites located immediately downstream of the promoter, a T7 bacteriophage RNA polymerase promoter positioned downstream of the SV40 splice sites, an SV40 polyadenylation signal downstream of the T7 promoter, and a polylinker between the T7 promoter and the polyadenylation signal. This vector thus contains all the regulatory elements required for expression of heterologous DNA in a mammalian host cell, wherein the heterologous DNA has been incorporated into the vector at the polylinker. In addition, because the T7 promoter is located just upstream of the polylinker, this plasmid can be used for synthesis of in vitro transcripts of heterologous DNA that has been subcloned into the vector at the polylinker. FIG. 1 also shows a restriction map of pCMV-T7-3. This plasmid is identical to pCMV-T7-2 except that the restriction sites in the polylinker are in the opposite order as compared to the order in which they occur in pCMV-T7-2.

A 1.7 kb SfiI (blunt-ended)/EcoRI DNA fragment containing nucleotides 27-1759 of SEQ ID No. 3 (i.e., the entire α₃ subunit coding sequence plus 12 nucleotides of 5' untranslated sequence and 206 nucleotides of 3' untranslated sequence) was ligated to EcoRVIEcoRI-digested pCMV-T7-2 to generate pCMV-KEα3. Plasmid pCMV-KEα3 was used for expression of the α₃ subunit in mammalian cells and for generating in vitro transcripts of the α₃ subunit DNA.

B. Constructs for Expression of a Human nNAChR β₄ Subunit

A 1.9 kb EcoRI DNA fragment containing nucleotides 1-1915 of SEQ ID No. 11 (i.e., the entire β₄ subunit coding sequence plus 86 nucleotides of 5' untranslated sequence and 332 nucleotides of 3' untranslated sequence) was ligated to EcoRI-digested pGEM7Zf(+) (Promega Catalog #P2251; Madison, Wis.). The resulting construct, KEβ4.6/pGEM, contains the T7 bacteriophage RNA polymerase promoter in operative association with two tandem β₄ subunit DNA inserts (in the same orientation) and was used in generating in vitro transcripts of the DNA.

The same 1.9 kb EcoRI DNA fragment containing nucleotides 1-1915 of SEQ ID No. 11 was ligated as a single insert to EcoRI-digested pCMV-T7-3 to generate pCMV-KEβ4. Plasmid pCMV-KEβ4 was used for expression of the β₄ subunit in mammalian cells and for generating in vitro transcripts of the β₄ subunit DNA.

C. Constructs for Expression of a Human nNAChR α₇ Subunit

Two pCMV-T7-2-based constructs were prepared for use in recombinant expression of a human neuronal nicotinic AChR α₇ subunit. The first construct, pCMV-KEα7.3, was prepared by ligating a 1.9 kb XhoI DNA fragment containing nucleotides 1-1876 of SEQ ID No. 7 (i.e., the entire α₇ subunit coding sequence plus 72 nucleotides of 5' untranslated sequence and 295 nucleotides of 3' untranslated sequence) to SalI-digested pCMV-T7-3. The second construct, pCMV-KEα7, was prepared by replacing the 5' untranslated sequence of the 1.9 kb XhoI α₇ subunit DNA fragment described above with a consensus ribosome binding site (5'-GCCACC-3'; see Kozak (1987) Nucl. Acids Res. 15:8125-8148). The resulting modified fragment was ligated as a 1.8 kb BglII/XhoI fragment with BglII/SalI-digested pCMV-T7-2 to generate pCMV-KEα7. Thus, in pCMV-KEα7, the translation initiation codon of the coding sequence of the α₇ subunit cDNA is preceded immediately by a consensus ribosome binding site.

D. Constructs for Expression of a Human nNAChR β₂ Subunit

DNA fragments encoding portions of a human neuronal nicotinic AchR β₂ subunit were ligated together to generate a full-length β₂ subunit coding sequence contained in plasmid pIBI24 (International Biotechnologies, Inc. (IBI), New Haven, Conn.). The resulting construct, Hβ2.1F, contains nucleotides 1-2450 of SEQ ID No. 9 (i.e., the entire β₂ subunit coding sequence, plus 266 nucleotides of 5' untranslated sequence and 675 nucleotides of 3' untranslated sequence) in operative association with the T7 promoter. Therefore, Hβ2.1F was used for synthesis of in vitro transcripts from the β₂ subunit DNA.

Since the 5' untranslated sequence of the β₂ subunit DNA contains a potential alternative translation initiation codon (ATG) beginning 11 nucleotides upstream (nucleotides 256-258 in SEQ ID No. 9) of the correct translation initiation codon (nucleotides 267-269 in SEQ ID No. 9), and because the use of the upstream ATG sequence to initiate translation of the β₂ DNA would result in the generation of an inoperative peptide (because the upstream ATG is not in the correct reading frame), an additional β₂ -encoding construct was prepared as follows. A 2.2 kb KspI/EcoRI DNA fragment containing nucleotides 262-2450 of SEQ ID No. 9 was ligated to pCMV-T7-2 in operative association with the T7 promoter of the plasmid to create pCMV-KEβ2. The β₂ subunit DNA contained in pCMV-KEβ2 retains only 5 nucleotides of 5' untranslated sequence upstream of the correct translation initiation codon.

EXAMPLE 3 Expression of Recombinant Human Nicotinic AChR in Oocytes

Xenopus oocytes were injected with in vitro transcripts prepared from constructs containing DNA encoding α₃, α₇, β₂ and β₄ subunits. Electrophysiological measurements of the oocyte transmembrane currents were made using the two-electrode voltage clamp technique (see, e.g., Stuhmer (1992) Meth. Enzymol. 207:319-339).

1. Preparation of in vitro transcripts

Recombinant capped transcripts of pCMV-KEα3, pCMV-KEβ2, KEβ4.6/pGEM and pCMV-KEβ4 were synthesized from linearized plasmids using the mCAP RNA Capping Kit (Cat. #200350 from Stratagene, Inc., La Jolla, Calif.). Recombinant capped transcripts of pCMV-KEα7, pCMV-KEα7.3 and Hβ2.1F were synthesized from linearized plasmids using the MEGAscript T7 in vitro transcription kit according to the capped transcript protocol provided by the manufacturer (Catalog #1334 from AMBION, Inc., Austin, Tex.). The mass of each synthesized transcript was determined by UV absorbance and the integrity of each transcript was determined by electrophoresis through an agarose gel.

2. Electrophysiology

Xenopus oocytes were injected with either 12.5, 50 or 125 ng of human nicotinic AChR subunit transcript per oocyte. The preparation and injection of oocytes were carried out as described by Dascal (1987) in Crit. Rev. Biochem. 22:317-387. Two-to-six days following mRNA injection, the oocytes were examined using the twoelectrode voltage clamp technique. The cells were bathed in Ringer's solution (115 mM NaCl, 2.5 mM KCl, 1.8 mM CaCl₂, 10 mM HEPES, pH 7.3) containing 1 μM atropine with or without 100 μM d-tubocurarine. Cells were voltage-clamped at -60 to -80 mV. Data were acquired with Axotape software at 2-5 Hz. The agonists acetylcholine (ACh), nicotine, and cytisine were added at concentrations ranging from 0.1 μM to 100 μM. The results of electrophysiological analyses of the oocytes are summarized in Table 1.

                  TABLE 1                                                          ______________________________________                                                       Number of                                                          Template, ng RNA oocytes  Current                                              injected responding Agonists Amplitude                                       ______________________________________                                         pCMV-KEα3, 12.5 ng                                                                     0 of 8    ACh,                                                       Nicotine                                                                     KEβ4.6/pGEM, 12.5 ng 0 of 9 ACh,                                            Nicotine                                                                     pCMV-KEα3, 12.5 ng 4 of 5 ACh, 20-550 nA                                 +  Nicotine                                                                    KEβ4.6/pGEM, 12.5 ng                                                      pCMV-KEα3, 12.5 ng 3 of 4 ACh, 20-300 nA                                 +  Cytisine,                                                                   KEβ4.6/pGEM, 12.5 ng  Nicotine                                            pCMV-KEα3, 125 ng 5 of 5 ACh, 200-500                                    +  Nicotine, nA                                                                and pCMV-KEβ4, 125 ng  Cytisine                                           pCMV-KEα3, 125 ng 6 of 6 ACh, 100-400                                    +  Nicotine, nA                                                                pCMV-KEβ4, 125 ng  Cytisine                                               pCMV-KEα7.3, 125 ng 3 of 15 ACh ˜20 nA                             pCMV-KEα7, 125 ng 11 of 11 ACh 20-250 nA                                 pCMV-KEα3, 12.5 ng 2 of 9 ACh, <10 nA                                    +  Nicotine                                                                    pCMV-KEβ2, 12.5 ng                                                        pCMV-KEα3, 125 ng 0 of 9 ACh,                                            +  Nicotine                                                                    pCMV-KEβ2, 125 ng                                                         pCMV-KEα3, 125 ng 13 of 16 ACh (100 μM) ˜20 nA                  +  ACh (300 μM) ˜80 nA                                                Hβ2.1F, 125 ng                                                          ______________________________________                                    

a. Oocytes Injected with α₃ and/or β₄ Transcripts

Oocytes that had been injected with 12.5 ng of the α₃ transcript or 12.5 ng of the 4 transcript did not respond to application of up to 100 MM ACh, nicotine or cytisine. Thus, it appears that these subunits do not form functional homomeric nicotinic AChR channels. By contrast, oocytes injected with 12.5 or 125 ng of the α₃ transcript and 12.5 ng or 125 ng of the β₄ transcript exhibited detectable inward currents in response to ACh, nicotine, and cytisine at the tested concentrations (0.1 μM to 10 μM). Some differences in the kinetics of the responses to cytisine compared to nicotine and ACh were observed. The relative potency of the agonists appeared to be cytisine >ACh > nicotine, which differs from the results of similar studies of oocytes injected with transcripts of the rat nicotinic ACHR α₃ and β₄ subunits (see, for example, Luetje et al. (1991) J. Neurosci. 11:837-845).

The responses to ACh and nicotine were reproducibly blocked by d-tubocurarine. For example, complete blockage of the response to ACh was observed in the presence of 100 μM d-tubocurarine. The inhibition appeared to be reversible. The responses to Ach, nicotine and cytisine were also at least partially blocked by 100 nM mecamylamine.

The current response of α₃ -β₄ -injected oocytes to 10 μM ACh was also examined in terms of membrane voltage. In these experiments, voltage steps were applied to the cells in the presence of ACh. The graph of current vs. voltage a ppe ared typ ical of responses observed for Na⁺, K⁺ -permeable channels. For example, the zero current level (reversal potential) is less than -40 mV. The contribution of Ca⁺⁺ flux to the total current can be ascertained by varying the calcium concentration in the external medium and taking multiple current measurements at different holding potentials around the reversal potential. Such studies indicate that the channel carrying the current generated in response to ACh treatment of α₃ -β₄ -injected oocytes is permeable to Na⁺, K⁺ and Ca⁺⁺.

b. Oocytes infected with α₇ subunit transcripts

As described in Example 1, two constructs were prepared for use in expressing the human neuronal nicotinic AChR α₇ subunit. Plasmid pCMV-KEα7.3 contains the α₇ subunit coding sequence with 72 nucleotides of 5' untranslated sequence upstream of the translation initiation codon. Plasmid pCMV-KEα7 contains the α₇ subunit coding sequence devoid of any 5' untranslated sequence and further contains a consensus ribosome binding site immediately upstream of the coding sequence.

Oocytes injected with 125 ng of α₇ transcript synthesized from pCMV-KEα7 displayed inward currents in response to 10 or 100 μM ACh. This response was blocked by 100 μM d-tubocurarine.

Oocytes injected with 125 ng of α₇ transcript synthesized from pCMV-KEα7.3 exhibited ACh-induced currents that were substantially weaker than those of oocytes injected with α₇ transcript synthesized from pCMV-KEα7. These results indicate that human neuronal nicotinic AChR α₇ subunit transcripts generated from α₇ subunit DNA containing a ribosome binding site in place of 5' untranslated sequence may be preferable for expression of the α₇ receptor in oocytes.

c. Oocytes injected with α₃ and β₂ subunit transcripts

As described in Example 1, two constructs were prepared for use in expressing the human neuronal nicotinic AChR β₂ subunit. Plasmid Hβ2.1F contains the β₂ subunit coding sequence with 266 nucleotides of 5' untranslated sequence upstream of the translation initiation codon. Plasmid pCMV-KEβ2 contains the β₂ subunit coding sequence and only 5 nucleotides of 5' untranslated sequence upstream of the translation initiation codon.

Oocytes injected with transcripts of pCMV-KEα3 and pCMV-KEβ2 displayed no current in response to nicotinic AChR agonists. In contrast, oocytes injected with transcripts of pCMV-KEα3 and Hβ2.1F displayed ˜20 nA inward currents in response to 100 μM ACh and ˜80 nA inward currents in response to 300 μM ACh. The current response was blocked by 100 μM d-tubocurarine. These results indicate that human neuronal nicotinic AChR β₂ subunit transcripts generated from β₂ subunit DNA containing 5' untranslated sequence may be preferable to transcripts generated from β₂ DNA containing only a small portion of 5' untranslated sequence for expression of the α₃ β₂ receptors in oocytes.

EXAMPLE 4 Recombinant Expression of Human nNAChR Subunits in Mammalian Cells

Human embryonic kidney (HEK) 293 cells were transiently and stably transfected with DNA encoding human neuronal nicotinic AChR α₃ and β₄, or α₇ subunits. Transient transfectants were analyzed for expression of nicotinic AChR using various assays, e.g., electrophysiological methods, Ca²⁺ -sensitive fluorescent indicator-based assays and [¹²⁵ I]-α-bungarotoxin-binding assays.

1. Transient Transfection of HEK Cells

Two transient transfections were performed. In one transfection, HEK cells were transiently co-transfected with DNA encoding α₃ (plasmid pCMV-KEα3) and β₄ (plasmid pCMV-KEβ4) subunits. In the other transfection, HEK cells were transiently transfected with DNA encoding the α₇ subunit (plasmid pCMV-KEα7). In both transfections, ˜2×10⁶ HEK cells were transiently transfected with 18 μg of the indicated plasmid(s) according to standard CaPO₄ transfection procedures [Wigler et al. (1979) Proc. Natl. Acad. Sci. USA 76:1373-1376]. In addition, 2 μg of plasmid pCMVβgal (Clontech Laboratories, Palo Alto, Calif.), which contains the Escherichia coil β-galactosidase gene fused to the CMV promoter, were co-transfected as a reporter gene for monitoring the efficiency of transfection. The transfectants were analyzed for β-galactosidase expression by measurement of β-galactosidase activity [Miller (1972) Experiments in Molecular Genetics, pp.352-355, Cold Spring Harbor Press]. Transfectants can also be analyzed for β-galactosidase expression by direct staining of the product of a reaction involving β-galactosidase and the X-gal substrate [Jones (1986) EMBO 5:3133-3142].

The efficiency of transfection of HEK cells with pCMV-KEα3/pCMV-KEβ4 was typical of standard efficiencies, whereas the efficiency of transfection of HEK cells with pCMV-KEα7 was below standard levels.

2. Stable Transfection of HEK Cells

HEK cells were transfected using the calcium phosphate transfection procedure [Current Protocols in Molecular Biology, Vol. 1, Wiley Inter-Science, Supplement 14, Unit 9.1.1-9.1.9 (1990)]. Ten-cm plates, each containing one-to-two million HEK cells were transfected with 1 ml of DNA/calcium phosphate precipitate containing 9.5 μg pCMV-KEα3, 9.5 μg pCMV-KEβ4 and 1 μg pSV2neo (as a selectable marker). After 14 days of growth in media containing 1 μg/ml G418, colonies had formed and were individually isolated by using cloning cylinders. The isolates were subjected to limiting dilution and screened to identify those that expressed the highest level of nicotinic AChR, as described below.

3. Analysis of Transfectants

a. Fluorescent indicator-based assays

Activation of the ligand-gated nicotinic AChR by agonists leads to an influx of cations, including Ca⁺⁺, through the receptor channel. Ca⁺⁺ entry into the cell through the channel can induce release of calcium contained in intracellular stores. Monovalent cation entry into the cell through the channel can also result in an increase in cytoplasmic Ca⁺⁺ levels through depolarization of the membrane and subsequent activation of voltage-dependent calcium channels. Therefore, methods of detecting transient increases in intracellular calcium concentration can be applied to the analysis of functional nicotinic AChR expression. One method for measuring intracellular calcium levels relies on calcium-sensitive fluorescent indicators.

Calcium-sensitive indicators, such as fluo-3 (Catalog No. F-1241, Molecular Probes, Inc., Eugene, Oreg.), are available as acetoxymethyl esters which are membrane permeable. When the acetoxymethyl ester form of the indicator enters a cell, the ester group is removed by cytosolic esterases, thereby trapping the free indicator in the cytosol. Interaction of the free indicator with calcium results in increased fluorescence of the indicator; therefore, an increase in the intracellular Ca²⁺ concentration of cells containing the indicator can be expressed directly as an increase in fluorescence. An automated fluorescence detection system for assaying nicotinic AChR has been described in commonly assigned pending U.S. patent application Ser. No. 07/812,254 and corresponding PCT Patent Application No. US92/11090.

HEK cells that were transiently or stably co-transfected with DNA encoding α₃ and β₄ subunits were analyzed for expression of functional recombinant nicotinic AChR using the automated fluorescent indicator-based assay. The assay procedure was as follows.

Untransfected HEK cells (or HEK cells transfected with pCMV-T7-2) and HEK cells that had been co-transfected with pCMV-KEα3 and pCMV-KEβ4 were plated in the wells of a 96-well microtiter dish and loaded with fluo-3 by incubation for 2 hours at 20° C. in a medium containing 20 μM fluo-3, 0.2% Pluronic F-127 in HBS (125 mM NaCl, 5 mM KCl, 1.8 mM CaCl₂, 0.62 mM MgSO₄, 6 mM glucose, 20 mM HEPES, pH 7.4). The cells were then washed with assay buffer (i.e., HBS). The antagonist d-tubocurarine was added to some of the wells at a final concentration of 10 μM. The microtiter dish was then placed into a fluorescence plate reader and the basal fluorescence of each well was measured and recorded before addition of 200 μM nicotine to the wells. The fluorescence of the wells was monitored repeatedly during a period of approximately 60 seconds following addition of nicotine.

The fluorescence of the untransfected HEK cells (or HEK cells transfected with pCMV-T7-2) did not change after addition of nicotine. In contrast, the fluorescence of the co-transfected cells, in the absence of d-tubocurarine, increased dramatically after addition of nicotine to the wells. This nicotine-stimulated increase in fluorescence was not observed in co-transfected cells that had been exposed to the antagonist d-tubocurarine. These results demonstrate that the co-transfected cells express functional recombinant AChR that are activated by nicotine and blocked by d-tubocurarine.

b. α-Bungarotoxin binding assays

HEK293 cells transiently transfected with pCMV-KEα7 were analyzed for [¹²⁵ I]-α-bungarotoxin (BgTx) binding. Both whole transfected cells and membranes prepared from transfected cells were examined in these assays. Rat brain membranes were included in the assays as a positive control.

Rat brain membranes were prepared according to the method of Hampson et al. (1987) J. Neurochem 49:1209. Membranes were prepared from the HEK cells transfected with pCMV-KEα7 and HEK cells transiently transfected with plasmid pUC19 only (negative control) according to the method of Perez-Reyes et al. (1989) Nature 340:233. Whole transfected and negative control cells were obtained by spraying the tissue culture plates with phosphate-buffered saline containing 0.1% (w/v) BSA. The cells were then centrifuged at low speed, washed once, resuspended in assay buffer (118 mM NaCl, 4.8 mM KCl, 2.5 mM CaCl₂, 1.2 mM MgSO₄, 20 mM HEPES, 0.1% (w/v)BSA, 0.05% (w/v) bacitracin and 0.5 mM PMSF, pH 7.5) and counted.

Specific binding of [¹²⁵ I]-α-BgTx to rat brain membranes was determined essentially as described by Marks et al. (1982) Molec. Pharmacol. 22:554-564, with several modifications. The membranes were washed twice in assay buffer. The assay was carried out in 12×75 mm polypropylene test tubes in a total volume of 0.5 ml assay buffer. The membranes were incubated 10 nM [¹²⁵ I]-α-BgTx (New England Nuclear, Boston, Mass.) for one hour at 37° C. The assay mixtures were then centrifuged at 2300×g for 10 minutes at 4° C. The supernatant was decanted and the pellets were washed twice with 2 ml aliquots of ice-cold assay buffer. The supernatants were decanted again and the radioactivity of the pellets was measured in a β-counter. Non-specific binding was determined in the presence of 1 μM unlabeled α-BgTx. Specific binding was determined by subtracting nonspecific binding from total binding. Specific binding of [¹²⁵ I]-α-BgTx to membranes prepared from transfected and negative control cells was determined as described for determining specific binding to rat brain membranes except that the assay buffer did not contain BSA, bacitracin and PMSF. Specific binding of [¹²⁵ I]-α-BgTx to transfected and negative control whole cells was determined basically as described for determining specific binding to rat brain membranes.

[¹²⁵ I]-α-BgTx binding was evaluated as a function of membrane concentration and as a function of incubation time. [¹²⁵ I]-α-BgTx binding to rat brain membranes increased in a linear fashion with increasing amounts of membrane (ranging between 25-500 μg). The overall signal-to-noise ratio of binding (i.e., ratio of total binding to non-specific binding) was 3:1. Although some binding of [¹²⁵ I]-α-BgTx to transfected cell membranes was detected, it was mostly non-specific binding and did not increase with increasing amounts of membrane. [¹²⁵ I]-α-BgTx binding to the transfectants and negative control cells appeared to be similar.

To monitor [¹²⁵ I]-α-BgTx binding to rat brain membranes and whole transfected and negative control cells, 300 μg of membrane or 500,000 cells were incubated with 1 nM or 10 nM [¹²⁵ I]-α-BgTx, respectively, at 37° C. for various times ranging from 0-350 min. Aliquots of assay mixture were transferred to 1.5 ml microfuge tubes at various times and centrifuged. The pellets were washed twice with assay buffer. [¹²⁵ I]-α-BgTx binding to rat brain membranes increased with time and was maximal after three hours. The binding profiles of the transfected and negative control cells were the same and differed from that of rat brain membranes.

EXAMPLE 5 Characterization of Cell Lines Expressing nNAChRs

Recombinant cell lines generated by transfection with DNA encoding human neuronal nicotinic AChRs, such as those described in Example 3, can be further characterized using one or more of the following methods.

A. Northern or slot blot analysis for expression of α- and/or β-subunit encoding messages

Total RNA is isolated from ˜1×10⁷ cells and 10-15 μg of RNA from each cell type is used for northern or slot blot hybridization analysis. The inserts from human neuronal NAChR-encoding plasmids can be nick-translated and used as probe. In addition, the β-actin gene sequence (Cleveland et al. (1980) Cell 20:95-105) can be nick-translated and used as a control probe on duplicate filters to confirm the presence or absence of RNA on each blot and to provide a rough standard for use in quantitating differences in α- or β-specific mRNA levels between cell lines. Typical northern and slot blot hybridization and wash conditions are as follows:

hybridization in 5× SSPE, 5× Denhardt's solution, 50% formamide, at 42° C. followed by washing in 0.2× SSPE, 0.1% SDS, at 65° C.

B. Nicotine-binding assay

Cell lines generated by transfection with human neuronal nicotinic AChR α- or α- and β-subunit-encoding DNA can be analyzed for their ability to bind nicotine, for example, as compared to control cell lines: neuronally-derived cell lines PC12 (Boulter et al., (1986), supra; ATCC #CRL1721) and IMR32 (Clementi, et al. (1986); Int. J. Neurochem. 47:291-297; ATCC #CCL127), and muscle-derived cell line BC3H1 (Patrick, et al., (1977); J. Biol. Chem. 252:2143-2153). Negative control cells (i.e., host cells from which the transfectants were prepared) are also included in the assay. The assay is conducted as follows:

Just prior to being assayed, transfected cells are removed from plates by scraping. Positive control cells used are PC12, BC3H1, and IMR32 (which had been starved for fresh media for seven days). Control cell lines are removed by rinsing in 37° C. assay buffer (50 mM Tris/HCl, 1 mM MgCl₂, 2 mM CaCl₂, 120 mM NaCl, 3 mM EDTA, 2 mg/ml BSA and 0.1% aprotinin at pH 7.4). The cells are 6 washed and resuspended to a concentration of 1×10⁶ /250 μl. To each plastic assay tube is added 250 μl of the cell solution, 15 nM ³ H-nicotine, with or without 1 mM unlabeled nicotine, and assay buffer to make a final volume of 500 μl. The assays for the transfected cell lines are incubated for 30 min at room temperature; the assays of the positive control cells are incubated for 2 min at 1° C. After the appropriate incubation time, 450 μl aliquots of assay volume are filtered through Whatman GF/C glass fiber filters which has been pretreated by incubation in 0.05% polyethyleneimine for 24 hours at 4° C. The filters are then washed twice, with 4 ml each wash, with ice cold assay buffer. After washing, the filters are dried, added to vials containing 5 ml scintillation fluid and radioactivity is measured.

C. ⁸⁶ Rb ion-flux assay

The ability of nicotine or nicotine agonists and antagonists to mediate the influx of ⁸⁶ Rb into transfected and control cells has been found to provide an indication of the presence of functional AChRs on the cell surface. The ⁸⁶ Rb ion-flux assay is conducted as follows:

1. The night before the experiment, cells are plated at 2×10⁶ per well (i.e., 2 ml per well) in a 6-well polylysine-coated plate.

2. The culture medium is decanted and the plate washed with 2 ml of assay buffer (50 mM HEPES, 260 mM sucrose, 5.4 mM KCl, 1.8 mM CaCl₂, 0.8 mM MgSO₄, 5.5. mM glucose) at room temperature.

3. The assay buffer is decanted and 1 ml of assay buffer, containing 3 μCi/ml ⁸⁶ Rb, with 5 mM ouabain and agonist or antagonist in a concentration to effect a maximum response, is added.

4. The plate is incubated on ice at 1° C. for 4 min.

5. The buffer is decanted into a waste container and each well was washed with 3 ml of assay buffer, followed by two washes of 2 ml each.

6. The cells are lysed with 2×0.5 ml of 0.2% SDS per well and transferred to a scintillation vial containing 5 ml of scintillation fluid.

7. The radioactivity contained in each vial is measured and the data calculated.

Positive control cells provided the following data in this assay:

    ______________________________________                                                  PC12         IMR32                                                                     Maximum            Maximum                                      EC.sub.50 response EC.sub.50 response                                        ______________________________________                                         Agonist                                                                          nicotine 52 μM 2.1X.sup.a 18 μM 7.7X.sup.a                               CCh* 35 μM 3.3X.sup.b 230 μM 7.6X.sup.c                                  cytisine 57 μM 3.6X.sup.d 14 μM 10X.sup.e                                Antagonist                                                                     d-tubocurarine 0.81 μM  2.5 μM                                           mecamylamine 0.42 μM  0.11 μM                                            hexamethonium nd.sup.f  22 μM                                               atropine 12.5 μM  43 μM                                                ______________________________________                                          *CCh = carbamylcholine                                                         .sup.a 200μM nicotine                                                       .sup.b 300μM CCh                                                            .sup.c 3mM CCh                                                                 .sup.d 1mM cytisine                                                            .sup.e 100μM cytisine                                                       .sup.f nd = not determined                                               

D. Electrophysiological Analysis of Mammalian Cells Transfected with Human Neuronal Nicotinic AChR Subunit-encoding DNA

Electrophysiological measurements may be used to assess the activity of recombinant receptors or to assess the ability of a test compound to potentiate, antagonize or otherwise modulate the magnitude and duration of the flow of cations through the ligand-gated recombinant AChR. The function of the expressed neuronal AChR can be assessed by a variety of electrophysiological techniques, including two-electrode voltage clamp and patch clamp methods. The cation-conducting channel intrinsic to the AChR opens in response to acetylcholine (ACh) or other nicotinic cholinergic agonists, permitting the flow of transmembrane current carried predominantly by sodium and potassium ions under physiological conditions. This current can be monitored directly by voltage clamp techniques. In preferred embodiments, transfected mammalian cells or injected oocytes are analyzed electrophysiologically for the presence of AChR agonist-dependent currents.

While the invention has been described in detail with reference to certain preferred embodiments thereof, it will be understood that modifications and variations are within the spirit and scope of that which is described and claimed.

SUMMARY OF SEQUENCES

Sequence ID No. 1 is a nucleotide sequence encoding an α₂ subunit of human neuronal nicotinic acetylcholine receptor, and the deduced amino acid sequence thereof.

Sequence ID No. 2 is the amino acid sequence of the α₂ subunit of human neuronal nicotinic acetylcholine receptor set forth in Sequence ID No. 1.

Sequence ID No. 3 is a nucleotide sequence encoding an α₃ subunit of human neuronal nicotinic acetylcholine receptor, and the deduced amino acid sequence thereof.

Sequence ID No. 4 is the amino acid sequence of the α₃ subunit of human neuronal nicotinic acetylcholine receptor set forth in Sequence ID No. 3.

Sequence ID No. 5 is a nucleotide sequence encoding an α₄ subunit of a human neuronal nicotinic acetylcholine receptor, and the deduced amino acid sequence thereof.

Sequence ID No. 6 is the amino acid sequence of the α₄ subunit of a human neuronal nicotinic acetylcholine receptor set forth in Sequence ID No. 5.

Sequence ID No. 7 is a nucleotide sequence encoding an α₇ subunit of human neuronal nicotinic acetylcholine receptor, and the deduced amino acid sequence thereof.

Sequence ID No. 8 is the amino acid sequence of the a subunit of human neuronal nicotinic acetylcholine receptor set forth in Sequence ID No. 7.

Sequence ID No. 9 is a nucleotide sequence encoding a β₂ subunit of human neuronal nicotinic acetylcholine receptor, and the deduced amino acid sequence thereof.

Sequence ID No. 10 is the amino acid sequence of the β₂ subunit of human neuronal nicotinic acetylcholine receptor set forth in Sequence ID No. 9.

Sequence ID No. 11 is a nucleotide sequence encoding a β₄ subunit of human neuronal nicotinic acetylcholine receptor, and the deduced amino acid sequence thereof.

Sequence ID No. 12 is the amino acid sequence of the β₄ subunit of human neuronal nicotinic acetylcholine receptor set forth in Sequence ID No. 11.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                    - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 12                                           - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 2068 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: both                                                         (D) TOPOLOGY: both                                                    - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 166..1752                                               - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - CAATGACCTG TTTTCTTCTG TAACCACAGG TTCGGTGGTG AGAGGAACCT TC -             #GCAGAATC     60                                                                  - - CAGCAGAATC CTCACAGAAT CCAGCAGCAG CTCTGCTGGG GACATGGTCC AT -             #GGTGCAAC    120                                                                  - - CCACAGCAAA GCCCTGACCT GACCTCCTGA TGCTCAGGAG AAGCCATGGG CC -             #CCTCCTGT    180                                                                  - - CCTGTGTTCC TGTCCTTCAC AAAGCTCAGC CTGTGGTGGC TCCTTCTGAC CC -             #CAGCAGGT    240                                                                  - - GGAGAGGAAG CTAAGCGCCC ACCTCCCAGG GCTCCTGGAG ACCCACTCTC CT -             #CTCCCAGT    300                                                                  - - CCCACGGCAT TGCCGCAGGG AGGCTCGCAT ACCGAGACTG AGGACCGGCT CT -             #TCAAACAC    360                                                                  - - CTCTTCCGGG GCTACAACCG CTGGGCGCGC CCGGTGCCCA ACACTTCAGA CG -             #TGGTGATT    420                                                                  - - GTGCGCTTTG GACTGTCCAT CGCTCAGCTC ATCGATGTGG ATGAGAAGAA CC -             #AAATGATG    480                                                                  - - ACCACCAACG TCTGGCTAAA ACAGGAGTGG AGCGACTACA AACTGCGCTG GA -             #ACCCCGCT    540                                                                  - - GATTTTGGCA ACATCACATC TCTCAGGGTC CCTTCTGAGA TGATCTGGAT CC -             #CCGACATT    600                                                                  - - GTTCTCTACA ACAAANNTGG GGAGTTTGCA GTGACCCACA TGACCAAGGC CC -             #ACCTCTTC    660                                                                  - - TCCACGGGCA CTGTGCACTG GGTGCCCCCG GCCATCTACA AGAGCTCCTG CA -             #GCATCGAC    720                                                                  - - GTCACCTTCT TCCCCTTCGA CCAGCAGAAC TGCAAGATGA AGTTTGGCTC CT -             #GGACTTAT    780                                                                  - - GACAAGGCCA AGATCGACCT GGAGCAGATG GAGCAGACTG TGGACCTGAA GG -             #ACTACTGG    840                                                                  - - GAGAGCGGCG AGTGGGCCAT CGTCAATGCC ACGGGCACCT ACAACAGCAA GA -             #AGTACGAC    900                                                                  - - TGCTGCGCCG AGATCTACCC CGACGTCACC TACGCCTTCG TCATCCGGCG GC -             #TGCCGCTC    960                                                                  - - TTCTACACCA TCAACCTCAT CATCCCCTGC CTGCTCATCT CCTGCCTCAC TG -             #TGCTGGTC   1020                                                                  - - TTCTACCTGC CCTCCGACTG CGGCGAGAAG ATCACGCTGT GCATTTCGGT GC -             #TGCTGTCA   1080                                                                  - - CTCACCGTCT TCCTGCTGCT CATCACTGAG ATCATCCCGT CCACCTCGCT GG -             #TCATCCCG   1140                                                                  - - CTCATCGGCG AGTACCTGCT GTTCACCATG ATCTTCGTCA CCCTGTCCAT CG -             #TCATCACC   1200                                                                  - - GTCTTCGTGC TCAATGTGGA CCACCGCTCC CCCAGCACCC ACACCATGCC CC -             #ACTGGGTG   1260                                                                  - - CGGGGGGCCC TTCTGGGCTG TGTGCCCCGG TGGCTTCTGA TGAACCGGCC CC -             #CACCACCC   1320                                                                  - - GTGGAGCTCT GCCACCCCCT ACGCCTGAAG CTCAGCCCCT CTTATCACTG GC -             #TGGAGAGC   1380                                                                  - - AACGTGGATG CCGAGGAGAG GGAGGTGGTG GTGGAGGAGG AGGACAGATG GG -             #CATGTGCA   1440                                                                  - - GGTCATGTGG CCCCCTCTGT GGGCACCCTC TGCAGCCACG GCCACCTGCA CT -             #CTGGGGCC   1500                                                                  - - TCAGGTCCCA AGGCTGAGGC TCTGCTGCAG GAGGGTGAGC TGCTGCTATC AC -             #CCCACATG   1560                                                                  - - CAGAAGGCAC TGGAAGGTGT GCACTACATT GCCGACCACC TGCGGTCTGA GG -             #ATGCTGAC   1620                                                                  - - TCTTCGGTGA AGGAGGACTG GAAGTATGTT GCCATGGTCA TCGACAGGAT CT -             #TCCTCTGG   1680                                                                  - - CTGTTTATCA TCGTCTGCTT CCTGGGGACC ATCGGCCTCT TTCTGCCTCC GT -             #TCCTAGCT   1740                                                                  - - GGAATGATCT GACTGCACCT CCCTCGAGCT GGCTCCCAGG GCAAAGGGGA GG -             #GTTCTTGG   1800                                                                  - - ATGTGGAAGG GCTTTGAACA ATGTTTAGAT TTGGAGATGA GCCCAAAGTG CC -             #AGGGAGAA   1860                                                                  - - CAGCCAGGTG AGGTGGGAGG TTGGAGAGCC AGGTGAGGTC TCTCTAAGTC AG -             #GCTGGGGT   1920                                                                  - - TGAAGTTTGG AGTCTGTCCG AGTTTGCAGG GTGCTGAGCT GTATGGTCCA GC -             #AGGGGAGT   1980                                                                  - - AATAAGGGCT CTTCCCGAAG GGGAGGAAGC GGGAGGCAGC GCCTGCACCT GA -             #TGTGGAGG   2040                                                                  - - TACAGAGCAG ATCTTCCCTA CCGGGGAG         - #                  - #                2068                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 528 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: unknown                                                 - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Met Gly Pro Ser Cys Pro Val Phe Leu Ser Ph - #e Thr Lys Leu Ser Leu       1               5   - #                10  - #                15                - - Trp Trp Leu Leu Leu Thr Pro Ala Gly Gly Gl - #u Glu Ala Lys Arg Pro                   20      - #            25      - #            30                    - - Pro Pro Arg Ala Pro Gly Asp Pro Leu Ser Se - #r Pro Ser Pro Thr Ala               35          - #        40          - #        45                        - - Leu Pro Gln Gly Gly Ser His Thr Glu Thr Gl - #u Asp Arg Leu Phe Lys           50              - #    55              - #    60                            - - His Leu Phe Arg Gly Tyr Asn Arg Trp Ala Ar - #g Pro Val Pro Asn Thr       65                  - #70                  - #75                  - #80         - - Ser Asp Val Val Ile Val Arg Phe Gly Leu Se - #r Ile Ala Gln Leu Ile                       85  - #                90  - #                95                - - Asp Val Asp Glu Lys Asn Gln Met Met Thr Th - #r Asn Val Trp Leu Lys                   100      - #           105      - #           110                   - - Gln Glu Trp Ser Asp Tyr Lys Leu Arg Trp As - #n Pro Ala Asp Phe Gly               115          - #       120          - #       125                       - - Asn Ile Thr Ser Leu Arg Val Pro Ser Glu Me - #t Ile Trp Ile Pro Asp           130              - #   135              - #   140                           - - Ile Val Leu Tyr Asn Lys Xaa Gly Glu Phe Al - #a Val Thr His Met Thr       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Lys Ala His Leu Phe Ser Thr Gly Thr Val Hi - #s Trp Val Pro Pro         Ala                                                                                              165  - #               170  - #               175              - - Ile Tyr Lys Ser Ser Cys Ser Ile Asp Val Th - #r Phe Phe Pro Phe Asp                   180      - #           185      - #           190                   - - Gln Gln Asn Cys Lys Met Lys Phe Gly Ser Tr - #p Thr Tyr Asp Lys Ala               195          - #       200          - #       205                       - - Lys Ile Asp Leu Glu Gln Met Glu Gln Thr Va - #l Asp Leu Lys Asp Tyr           210              - #   215              - #   220                           - - Trp Glu Ser Gly Glu Trp Ala Ile Val Asn Al - #a Thr Gly Thr Tyr Asn       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Ser Lys Lys Tyr Asp Cys Cys Ala Glu Ile Ty - #r Pro Asp Val Thr         Tyr                                                                                              245  - #               250  - #               255              - - Ala Phe Val Ile Arg Arg Leu Pro Leu Phe Ty - #r Thr Ile Asn Leu Ile                   260      - #           265      - #           270                   - - Ile Pro Cys Leu Leu Ile Ser Cys Leu Thr Va - #l Leu Val Phe Tyr Leu               275          - #       280          - #       285                       - - Pro Ser Asp Cys Gly Glu Lys Ile Thr Leu Cy - #s Ile Ser Val Leu Leu           290              - #   295              - #   300                           - - Ser Leu Thr Val Phe Leu Leu Leu Ile Thr Gl - #u Ile Ile Pro Ser Thr       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Ser Leu Val Ile Pro Leu Ile Gly Glu Tyr Le - #u Leu Phe Thr Met         Ile                                                                                              325  - #               330  - #               335              - - Phe Val Thr Leu Ser Ile Val Ile Thr Val Ph - #e Val Leu Asn Val Asp                   340      - #           345      - #           350                   - - His Arg Ser Pro Ser Thr His Thr Met Pro Hi - #s Trp Val Arg Gly Ala               355          - #       360          - #       365                       - - Leu Leu Gly Cys Val Pro Arg Trp Leu Leu Me - #t Asn Arg Pro Pro Pro           370              - #   375              - #   380                           - - Pro Val Glu Leu Cys His Pro Leu Arg Leu Ly - #s Leu Ser Pro Ser Tyr       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - His Trp Leu Glu Ser Asn Val Asp Ala Glu Gl - #u Arg Glu Val Val         Val                                                                                              405  - #               410  - #               415              - - Glu Glu Glu Asp Arg Trp Ala Cys Ala Gly Hi - #s Val Ala Pro Ser Val                   420      - #           425      - #           430                   - - Gly Thr Leu Cys Ser His Gly His Leu His Se - #r Gly Ala Ser Gly Pro               435          - #       440          - #       445                       - - Lys Ala Glu Ala Leu Leu Gln Glu Gly Glu Le - #u Leu Leu Ser Pro His           450              - #   455              - #   460                           - - Met Gln Lys Ala Leu Glu Gly Val His Tyr Il - #e Ala Asp His Leu Arg       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Ser Glu Asp Ala Asp Ser Ser Val Lys Glu As - #p Trp Lys Tyr Val         Ala                                                                                              485  - #               490  - #               495              - - Met Val Ile Asp Arg Ile Phe Leu Trp Leu Ph - #e Ile Ile Val Cys Phe                   500      - #           505      - #           510                   - - Leu Gly Thr Ile Gly Leu Phe Leu Pro Pro Ph - #e Leu Ala Gly Met Ile               515          - #       520          - #       525                       - -  - - (2) INFORMATION FOR SEQ ID NO:3:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1756 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: both                                                         (D) TOPOLOGY: both                                                    - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 39..1553                                                - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                - - CCGACCGTCC GGGTCCGCGG CCAGCCCGGC CACCAGCCAT GGGCTCTGGC CC -              #GCTCTCGC     60                                                                  - - TGCCCCTGGC GCTGTCGCCG CCGCGGCTGC TGCTGCTGCT GCTGTCTCTG CT -             #GCCAGTGG    120                                                                  - - CCAGGGCCTC AGAGGCTGAG CACCGTCTAT TTGAGCGGCT GTTTGAAGAT TA -             #CAATGAGA    180                                                                  - - TCATCCGGCC TGTGGCCAAC GTGTCTGACC CAGTCATCAT CCATTTCGAG GT -             #GTCCATGT    240                                                                  - - CTCAGCTGGT GAAGGTGGAT GAAGTAAACC AGATCATGGA GACCAACCTG TG -             #GCTCAAGC    300                                                                  - - AAATCTGGMA TGACTACAAG CTGAAGTGGA ACCCCTCTGA CTATGGTGGG GC -             #AGAGTTCA    360                                                                  - - TGCGTGTCCC TGCACAGAAG ATCTGGAAGC CAGACATTGT GCTGTATAAC AA -             #TGCTGTTG    420                                                                  - - GGGATTTCCA GGTGGACGAC AAGACCAAAG CCTTACTCAA GTACACTGGG GA -             #GGTGACTT    480                                                                  - - GGATACCTCC GGCCATCTTT AAGAGCTCCT GTAAAATCGA CGTGACCTAC TT -             #CCCGTTTG    540                                                                  - - ATTACCAAAA CTGTACCATG AAGTTCGGTT CCTGGTCCTA CGATAAGGCG AA -             #AATCGACC    600                                                                  - - TGGTCCTGAT CGGCTCTTCC ATGAACCTCA AGGACTATTG GGAGAGCGGC GA -             #GTGGGCCA    660                                                                  - - TCATCAAAGC CCCAGGYTAT AACCACGACA TCAAGTACAA CTGCTGCGAG GA -             #GATCTACC    720                                                                  - - CCGACATCAC ATACTCGCTG ATCATCCGGC GGCTGTCGTT GTTCTACACC AT -             #CATCCTCA    780                                                                  - - TCATCCCCTG GCTGATCATC TCCTTCATCA CTGTGGTCGT CTTCTACCTG CC -             #CTCCGACT    840                                                                  - - GCGGTGAGAA GGTGACCCTG TGCATTTCTG TCCTCCTCTC CCTGACGGTG TT -             #TCTCCTGG    900                                                                  - - TGATCACTGA GACCATCCCT TCCACCTCGC TGGTCATCCC CCTGATTGGA GA -             #GTACCTCC    960                                                                  - - TGTTCACCAT GATTTTTGTA ACCTTGTCCA TCGCCATCAC CGTCTTCGTG CT -             #CAACGTGC   1020                                                                  - - ACTACAGAAC CCCGACGACA CACACAATGC CCTCATGGGT GAAGACTGTA TT -             #CTTGAACC   1080                                                                  - - TGCTCCCCAG GGTCATGTTC ATGACCAGGC CAACAAGCAA CGAGGGCAAC GC -             #TCAGAAGC   1140                                                                  - - CGAGGCCCCT CTACGGTGCC GAGCTCTCAA ATCTGAATTG CTTCAGCCGC GC -             #AGAGTCCA   1200                                                                  - - WAGGCTGCAA GGAGGGCTAC CCCTGCCAGG ACGGGATGTG TGGTTACTGC CA -             #CCACCGCA   1260                                                                  - - GGATAAAAAT CTCCAATTTC AGTGCTAACC TCACGAGAAG CTCTAGTTCT GA -             #ATCTGTTG   1320                                                                  - - ATGCTGTGCT GTCCCTCTCT GCTTTGTCAC CAGAAATCAA AGAAGCCATC CA -             #AAGTGTCA   1380                                                                  - - AGTATATTGC TGAAAATATG AAAGCACAAA ATGAAGCCAA AGAGATTCAA GA -             #TGATTGGA   1440                                                                  - - AGTATGTTGC CATGGTGATT GATCGCATTT TTCTGTGGGT TTTCACCCTG GT -             #GTGCATTC   1500                                                                  - - TAGGGACAGA AGGATTGTTT CTGCAACCCC TGATGGCCAG GGAAGATGCA TA -             #AGCACTAA   1560                                                                  - - GCTGTGTGTC TGTCTGGGAG AGTTCCCTGT GTCAGAGAAG AGGGAGGCTG CT -             #TCCTAGTA   1620                                                                  - - AGAACGTACT TTCTGTTATC AAGCTACCAG CTTTGTTTTT GGCATTTCGA GG -             #TTTACTTA   1680                                                                  - - TTTTCCACTT ATCTTGGAAT CATGCGCGAM MAAATGTCAA GAGTATTTAT TA -             #CCGATAAA   1740                                                                  - - TGAACATTTA ACTAGC             - #                  - #                       - #  1756                                                                   - -  - - (2) INFORMATION FOR SEQ ID NO:4:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 504 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: unknown                                                 - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                - - Met Gly Ser Gly Pro Leu Ser Leu Pro Leu Al - #a Leu Ser Pro Pro Arg       1               5   - #                10  - #                15                - - Leu Leu Leu Leu Leu Leu Ser Leu Leu Pro Va - #l Ala Arg Ala Ser Glu                   20      - #            25      - #            30                    - - Ala Glu His Arg Leu Phe Glu Arg Leu Phe Gl - #u Asp Tyr Asn Glu Ile               35          - #        40          - #        45                        - - Ile Arg Pro Val Ala Asn Val Ser Asp Pro Va - #l Ile Ile His Phe Glu           50              - #    55              - #    60                            - - Val Ser Met Ser Gln Leu Val Lys Val Asp Gl - #u Val Asn Gln Ile Met       65                  - #70                  - #75                  - #80         - - Glu Thr Asn Leu Trp Leu Lys Gln Ile Trp Xa - #a Asp Tyr Lys Leu Lys                       85  - #                90  - #                95                - - Trp Asn Pro Ser Asp Tyr Gly Gly Ala Glu Ph - #e Met Arg Val Pro Ala                   100      - #           105      - #           110                   - - Gln Lys Ile Trp Lys Pro Asp Ile Val Leu Ty - #r Asn Asn Ala Val Gly               115          - #       120          - #       125                       - - Asp Phe Gln Val Asp Asp Lys Thr Lys Ala Le - #u Leu Lys Tyr Thr Gly           130              - #   135              - #   140                           - - Glu Val Thr Trp Ile Pro Pro Ala Ile Phe Ly - #s Ser Ser Cys Lys Ile       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Asp Val Thr Tyr Phe Pro Phe Asp Tyr Gln As - #n Cys Thr Met Lys         Phe                                                                                              165  - #               170  - #               175              - - Gly Ser Trp Ser Tyr Asp Lys Ala Lys Ile As - #p Leu Val Leu Ile Gly                   180      - #           185      - #           190                   - - Ser Ser Met Asn Leu Lys Asp Tyr Trp Glu Se - #r Gly Glu Trp Ala Ile               195          - #       200          - #       205                       - - Ile Lys Ala Pro Gly Tyr Asn His Asp Ile Ly - #s Tyr Asn Cys Cys Glu           210              - #   215              - #   220                           - - Glu Ile Tyr Pro Asp Ile Thr Tyr Ser Leu Il - #e Ile Arg Arg Leu Ser       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Leu Phe Tyr Thr Ile Ile Leu Ile Ile Pro Tr - #p Leu Ile Ile Ser         Phe                                                                                              245  - #               250  - #               255              - - Ile Thr Val Val Val Phe Tyr Leu Pro Ser As - #p Cys Gly Glu Lys Val                   260      - #           265      - #           270                   - - Thr Leu Cys Ile Ser Val Leu Leu Ser Leu Th - #r Val Phe Leu Leu Val               275          - #       280          - #       285                       - - Ile Thr Glu Thr Ile Pro Ser Thr Ser Leu Va - #l Ile Pro Leu Ile Gly           290              - #   295              - #   300                           - - Glu Tyr Leu Leu Phe Thr Met Ile Phe Val Th - #r Leu Ser Ile Ala Ile       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Thr Val Phe Val Leu Asn Val His Tyr Arg Th - #r Pro Thr Thr His         Thr                                                                                              325  - #               330  - #               335              - - Met Pro Ser Trp Val Lys Thr Val Phe Leu As - #n Leu Leu Pro Arg Val                   340      - #           345      - #           350                   - - Met Phe Met Thr Arg Pro Thr Ser Asn Glu Gl - #y Asn Ala Gln Lys Pro               355          - #       360          - #       365                       - - Arg Pro Leu Tyr Gly Ala Glu Leu Ser Asn Le - #u Asn Cys Phe Ser Arg           370              - #   375              - #   380                           - - Ala Glu Ser Xaa Gly Cys Lys Glu Gly Tyr Pr - #o Cys Gln Asp Gly Met       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Cys Gly Tyr Cys His His Arg Arg Ile Lys Il - #e Ser Asn Phe Ser         Ala                                                                                              405  - #               410  - #               415              - - Asn Leu Thr Arg Ser Ser Ser Ser Glu Ser Va - #l Asp Ala Val Leu Ser                   420      - #           425      - #           430                   - - Leu Ser Ala Leu Ser Pro Glu Ile Lys Glu Al - #a Ile Gln Ser Val Lys               435          - #       440          - #       445                       - - Tyr Ile Ala Glu Asn Met Lys Ala Gln Asn Gl - #u Ala Lys Glu Ile Gln           450              - #   455              - #   460                           - - Asp Asp Trp Lys Tyr Val Ala Met Val Ile As - #p Arg Ile Phe Leu Trp       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Val Phe Thr Leu Val Cys Thr Leu Gly Thr Gl - #u Gly Leu Phe Leu         Gln                                                                                              485  - #               490  - #               495              - - Pro Leu Met Ala Arg Glu Asp Ala                                                       500                                                                 - -  - - (2) INFORMATION FOR SEQ ID NO:5:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 2374 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: both                                                         (D) TOPOLOGY: both                                                    - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 184..2067                                               - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                - - TCCACAAGCC GGCGCTCGCT GCGGCGCCGC CGCCGCGCCG CGCGCCACAG GA -              #GAAGGCGA     60                                                                  - - GCCGGGCCCG GCGGCCGAAG CGGCCCGCGA GGCGCGGGAG GCATGAAGTT GG -             #GCGCGCAC    120                                                                  - - GGGCCTCGAA GCGGCGGGGA GCCGGGAGCC GCCCGCATCT AGAGCCCGCG AG -             #GTGCGTGC    180                                                                  - - GCCATGGAGC TAGGGGGCCC CGGAGCGCCG CGGCTGCTGC CGCCGCTGCT GC -             #TGCTTCTG    240                                                                  - - GGGACCGGCC TCCTGCGCGC CAGCAGCCAT GTGGAGACCC GGGCCCACGC CG -             #AGGAGCGG    300                                                                  - - CTCCTGAAGA AACTCTTCTC CGGTTACAAC AAGTGGTCCC GACCCGTGGC CA -             #ACATCTCG    360                                                                  - - GACGTGGTCC TCGTCCGCTT CGGCCTGTCC ATCGCTCAGC TCATTGACGT GG -             #ATGAGAAG    420                                                                  - - AACCAGATGA TGACCACGAA CGTCTGGGTG AAGCAGGAGT GGCACGACTA CA -             #AGCTGCGC    480                                                                  - - TGGGACCCAG CTGACTATGA GAATGTCACC TCCATCCGCA TCCCCTCCGA GC -             #TCATCTGG    540                                                                  - - CGGCCGGACA TCGCCCTCTA CAACAATGCT GACGGGGACT TCGCGGCCAC CC -             #ACCTGACC    600                                                                  - - AAGGCCCACC TGTTCCATGA CGGGCGGGTG CAGCGGACTC CCCCGGCCAT TT -             #ACAAGAGC    660                                                                  - - TCCTGCAGCA TCGACGTCAC CTTCTTCCCC TTCGACCAGC AGAACTGCAC CA -             #TGAAATTC    720                                                                  - - GGCTCCTGGA CCTACGACAA GGCCAAGATC GACCTGGTGA ACATGCACAG CC -             #GCGTGGAC    780                                                                  - - CAGCTGGACT TCTGGGAGAG TGGCGAGTGG CTCATCGCGG ACGCCGYGGG CA -             #CCTACAAC    840                                                                  - - ACCAGGAAGT ACGAGTGCTG CGCCGAGATC TACCCGGACA TCACCTATGC CT -             #ACGCCATC    900                                                                  - - CGGCGGCTGC CGCTCTTCTG CACCATCAAC CTCATCATCC CCTGGCTGCT CA -             #TCTCCTGC    960                                                                  - - CTCACCGCGC TGGTCTTCTA CCTGCCCTCC GAGTGTGGCG AGAAGATCAC GC -             #TGTGCATC   1020                                                                  - - TCCGCGCTGC TGTCGCTCAC CGGCTTCCTG CTGCTCATCA CCGAGATCAT CC -             #CGCCCACC   1080                                                                  - - TCACTGGTCA TCCCACTCAT CGGCGAGTAC CTGCTGTTCA CCATGATCTT CG -             #TCACCCTG   1140                                                                  - - TCCATCGCCA TCACGGTCTT CGTGCTCAAC GTGCACCACC GCTCGCCACG CA -             #CGCACACC   1200                                                                  - - ATGCCCACCT GGGTACGCAG CGTCTTCCTG GACATCGTGC CACGCCTGCT CC -             #TCATGAAG   1260                                                                  - - CGGCCGTCCG TGGTCAAGGA CAATTGCCGG CGGCTCATCG AGTCCATGCA TA -             #AGATGGCC   1320                                                                  - - AGTGCCCCGC GCTTCTGGCC CGAGCCAGAA GGGGAGCCCC CTGCCACGAG CG -             #GCACCCAG   1380                                                                  - - AGCCTGCACC CTCCCTCACC GCCCTTCTGC GTCCCCCTGG ATGTGCCGGC TG -             #AGCCTGGG   1440                                                                  - - CCTTCCTGCA AGTCACCCTC CGACCAGCTC CCTCCTCAGA AGCCCCTGGA AG -             #CTGAGAAA   1500                                                                  - - GACAGCCCCC ACCCCTCGCC TGGACCCTGC CGCCCGCCCC ACGGCACCCA GG -             #CACCAGGG   1560                                                                  - - CTGGCCAAAG CCAGGTCCCT CAGCGTCCAG CACATGTCCA GCCCTGGCGA AG -             #CGGTGGAA   1620                                                                  - - GGCGGCGTCC GGTGCCGGTC TCGGAGCATC CAGTACTGTG TTCCCCGAGA CG -             #ATGCCGCC   1680                                                                  - - CCCGAGGCAG ATGGCCAGGC TKCCGGCGCC CTGGCCTCTC GCAACAGCCA CT -             #CGGCTGAG   1740                                                                  - - CTCCCACCCC CAGACCAGCC CTCTCCGTGC AAATGCACAT GCAAGAAGGA GC -             #CCTCTTCG   1800                                                                  - - GTGTCCCCGA GCGCCRCGGT CAAGACCCGC AGCACCAAAG CGCCGCCGCC GC -             #ACCTGCCC   1860                                                                  - - CTGTCGCCGG CCCTGAGCCG GGCGGTGGAG GGCGTCCAGT ACATTGCAGA CC -             #ACCTGAAG   1920                                                                  - - GCCGAAGACA CAGACTTCTC GGTGAAGGAG GACTGGAAGT ACGTGGCCAT GG -             #TCATCGAC   1980                                                                  - - CGCATCTTCC TCTGGATGTT CATCATCGTC TGCCTGCTGG GGACGGTGGG CC -             #TCTTCCTG   2040                                                                  - - CCGCCCTGGC TGGCTGGCAT GATCTAGGAA GGGACCGGGA GCCTGCGTGG CC -             #TGGGGCTG   2100                                                                  - - CCGCGCACGG GGCCAGCATC CATGCGGCCG GCCTGGGGCC GGGCTGGCTT CT -             #CCCTGGAC   2160                                                                  - - TCTGTGGGGC CACACGTTTG CCAAATTTCC CTYCCTGTTC TGTGTCTGCT GT -             #AAGACGGC   2220                                                                  - - CTTGGACGGC GACACGGCCT CTGGGGAGAC CGAGTGTGGA GCTGCTTCCA GT -             #TGGACTCT   2280                                                                  - - SGCCTCAGNA GGCAGCGGCT TGGAGCAGAG GTGGCGGTCG CCGCCTYCTA CC -             #TGCAGGAC   2340                                                                  - - TCGGGCTAAG TCCAGCTCTC CCCCTGCGCA GCCC       - #                  -      #      2374                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:6:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 627 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: unknown                                                 - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                - - Met Glu Leu Gly Gly Pro Gly Ala Pro Arg Le - #u Leu Pro Pro Leu Leu       1               5   - #                10  - #                15                - - Leu Leu Leu Gly Thr Gly Leu Leu Arg Ala Se - #r Ser His Val Glu Thr                   20      - #            25      - #            30                    - - Arg Ala His Ala Glu Glu Arg Leu Leu Lys Ly - #s Leu Phe Ser Gly Tyr               35          - #        40          - #        45                        - - Asn Lys Trp Ser Arg Pro Val Ala Asn Ile Se - #r Asp Val Val Leu Val           50              - #    55              - #    60                            - - Arg Phe Gly Leu Ser Ile Ala Gln Leu Ile As - #p Val Asp Glu Lys Asn       65                  - #70                  - #75                  - #80         - - Gln Met Met Thr Thr Asn Val Trp Val Lys Gl - #n Glu Trp His Asp Tyr                       85  - #                90  - #                95                - - Lys Leu Arg Trp Asp Pro Ala Asp Tyr Glu As - #n Val Thr Ser Ile Arg                   100      - #           105      - #           110                   - - Ile Pro Ser Glu Leu Ile Trp Arg Pro Asp Il - #e Ala Leu Tyr Asn Asn               115          - #       120          - #       125                       - - Ala Asp Gly Asp Phe Ala Ala Thr His Leu Th - #r Lys Ala His Leu Phe           130              - #   135              - #   140                           - - His Asp Gly Arg Val Gln Arg Thr Pro Pro Al - #a Ile Tyr Lys Ser Ser       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Cys Ser Ile Asp Val Thr Phe Phe Pro Phe As - #p Gln Gln Asn Cys         Thr                                                                                              165  - #               170  - #               175              - - Met Lys Phe Gly Ser Trp Thr Tyr Asp Lys Al - #a Lys Ile Asp Leu Val                   180      - #           185      - #           190                   - - Asn Met His Ser Arg Val Asp Gln Leu Asp Ph - #e Trp Glu Ser Gly Glu               195          - #       200          - #       205                       - - Trp Leu Ile Ala Asp Ala Xaa Gly Thr Tyr As - #n Thr Arg Lys Tyr Glu           210              - #   215              - #   220                           - - Cys Cys Ala Glu Ile Tyr Pro Asp Ile Thr Ty - #r Ala Tyr Ala Ile Arg       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Arg Leu Pro Leu Phe Cys Thr Ile Asn Leu Il - #e Ile Pro Trp Leu         Leu                                                                                              245  - #               250  - #               255              - - Ile Ser Cys Leu Thr Ala Leu Val Phe Tyr Le - #u Pro Ser Glu Cys Gly                   260      - #           265      - #           270                   - - Glu Lys Ile Thr Leu Cys Ile Ser Ala Leu Le - #u Ser Leu Thr Gly Phe               275          - #       280          - #       285                       - - Leu Leu Leu Ile Thr Glu Ile Ile Pro Pro Th - #r Ser Leu Val Ile Pro           290              - #   295              - #   300                           - - Leu Ile Gly Glu Tyr Leu Leu Phe Thr Met Il - #e Phe Val Thr Leu Ser       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Ile Ala Ile Thr Val Phe Val Leu Asn Val Hi - #s His Arg Ser Pro         Arg                                                                                              325  - #               330  - #               335              - - Thr His Thr Met Pro Thr Trp Val Arg Ser Va - #l Phe Leu Asp Ile Val                   340      - #           345      - #           350                   - - Pro Arg Leu Leu Leu Met Lys Arg Pro Ser Va - #l Val Lys Asp Asn Cys               355          - #       360          - #       365                       - - Arg Arg Leu Ile Glu Ser Met His Lys Met Al - #a Ser Ala Pro Arg Phe           370              - #   375              - #   380                           - - Trp Pro Glu Pro Glu Gly Glu Pro Pro Ala Th - #r Ser Gly Thr Gln Ser       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Leu His Pro Pro Ser Pro Pro Phe Cys Val Pr - #o Leu Asp Val Pro         Ala                                                                                              405  - #               410  - #               415              - - Glu Pro Gly Pro Ser Cys Lys Ser Pro Ser As - #p Gln Leu Pro Pro Gln                   420      - #           425      - #           430                   - - Lys Pro Leu Glu Ala Glu Lys Asp Ser Pro Hi - #s Pro Ser Pro Gly Pro               435          - #       440          - #       445                       - - Cys Arg Pro Pro His Gly Thr Gln Ala Pro Gl - #y Leu Ala Lys Ala Arg           450              - #   455              - #   460                           - - Ser Leu Ser Val Gln His Met Ser Ser Pro Gl - #y Glu Ala Val Glu Gly       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Gly Val Arg Cys Arg Ser Arg Ser Ile Gln Ty - #r Cys Val Pro Arg         Asp                                                                                              485  - #               490  - #               495              - - Asp Ala Ala Pro Glu Ala Asp Gly Gln Ala Xa - #a Gly Ala Leu Ala Ser                   500      - #           505      - #           510                   - - Arg Asn Ser His Ser Ala Glu Leu Pro Pro Pr - #o Asp Gln Pro Ser Pro               515          - #       520          - #       525                       - - Cys Lys Cys Thr Cys Lys Lys Glu Pro Ser Se - #r Val Ser Pro Ser Ala           530              - #   535              - #   540                           - - Xaa Val Lys Thr Arg Ser Thr Lys Ala Pro Pr - #o Pro His Leu Pro Leu       545                 5 - #50                 5 - #55                 5 -       #60                                                                               - - Ser Pro Ala Leu Ser Arg Ala Val Glu Gly Va - #l Gln Tyr Ile Ala         Asp                                                                                              565  - #               570  - #               575              - - His Leu Lys Ala Glu Asp Thr Asp Phe Ser Va - #l Lys Glu Asp Trp Lys                   580      - #           585      - #           590                   - - Tyr Val Ala Met Val Ile Asp Arg Ile Phe Le - #u Trp Met Phe Ile Ile               595          - #       600          - #       605                       - - Val Cys Leu Leu Gly Thr Val Gly Leu Phe Le - #u Pro Pro Trp Leu Ala           610              - #   615              - #   620                           - - Gly Met Ile                                                               625                                                                             - -  - - (2) INFORMATION FOR SEQ ID NO:7:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1876 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: both                                                         (D) TOPOLOGY: both                                                    - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 73..1581                                                - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                - - GGCCGCAGGC GCAGGCCCGG GCGACAGCCG AGACGTGGAG CGCGCCGGCT CG -              #CTGCAGCT     60                                                                  - - CCGGGACTCA ACATGCGCTG CTCGCCGGGA GGCGTCTGGC TGGCGCTGGC CG -             #CGTCGCTC    120                                                                  - - CTGCACGTGT CCCTGCAAGG CGAGTTCCAG AGGAAGCTTT ACAAGGAGCT GG -             #TCAAGAAC    180                                                                  - - TACAATCCCT TGGAGAGGCC CGTGGCCAAT GACTCGCAAC CACTCACCGT CT -             #ACTTCTCC    240                                                                  - - CTGAGCCTCC TGCAGATCAT GGACGTGGAT GAGAAGAACC AAGTTTTAAC CA -             #CCAACATT    300                                                                  - - TGGCTGCAAA TGTCTTGGAC AGATCACTAT TTACAGTGGA ATGTGTCAGA AT -             #ATCCAGGG    360                                                                  - - GTGAAGACTG TTCGTTTCCC AGATGGCCAG ATTTGGAAAC CAGACATTCT TC -             #TCTATAAC    420                                                                  - - AGTGCTGATG AGCGCTTTGA CGCCACATTC CACACTAACG TGTTGGTGAA TT -             #CTTCTGGG    480                                                                  - - CATTGCCAGT ACCTGCCTCC AGGCATATTC AAGAGTTCCT GCTACATCGA TG -             #TACGCTGG    540                                                                  - - TTTCCCTTTG ATGTGCAGCA CTGCAAACTG AAGTTTGGGT CCTGGTCTTA CG -             #GAGGCTGG    600                                                                  - - TCCTTGGATC TGCAGATGCA GGAGGCAGAT ATCAGTGGCT ATATCCCCAA TG -             #GAGAATGG    660                                                                  - - GACCTAGTGG GAATCCCCGG CAAGAGGAGT GAAAGGTTCT ATGAGTGCTG CA -             #AAGAGCCC    720                                                                  - - TACCCCGATG TCACCTTCAC AGTGACCATG CGCCGCAGGA CGCTCTACTA TG -             #GCCTCAAC    780                                                                  - - CTGCTGATCC CCTGTGTGCT CATCTCCGCC CTCGCCCTGC TGGTGTTCCT GC -             #TTCCTGCA    840                                                                  - - GATTCCGGGG AGAAGATTTC CCTGGGGATA ACAGTCTTAC TCTCTCTTAC CG -             #TCTTCATG    900                                                                  - - CTGCTCGTGG CTGAGATCAT GCCCGCAACA TCCGATTCGG TACCATTGAT AG -             #CCCAGTAC    960                                                                  - - TTCGCCAGCA CCATGATCAT CGTGGGCCTC TCGGTGGTGG TGACGGTGAT CG -             #TGCTGCAG   1020                                                                  - - TACCACCACC ACGACCCCGA CGGGGGCAAG ATGCCCAAGT GGACCAGAGT CA -             #TCCTTCTG   1080                                                                  - - AACTGGTGCG CGTGGTTCCT SCGAATGAAG AGGCCCGGGG AGGACAAGGT GC -             #GCCCGGCC   1140                                                                  - - TGCCAGCACA AGCAGCGGCG CTGCAGCCTG GCCAGTGTGG AGATGAGCGC CG -             #TGGCGCCG   1200                                                                  - - CCGCCCGCCA GCAACGGGAA CCTGCTGTAC ATCGGCTTCC GCGGCCTGGA CG -             #GCGTGCAC   1260                                                                  - - TGTGTCCCGA CCCCCGACTC TGGGGTAGTG TGTGGCCGCA TGGCCTGCTC CC -             #CCACGCAC   1320                                                                  - - GATGAGCACC TCCTGCACGG CGGGCAACCC CCCGAGGGGG ACCCGGACTT GG -             #CCAAGATC   1380                                                                  - - CTGGAGGAGG TCCGCTACAT TGCCAATCGC TTCCGCTGCC AGGACGAAAG CG -             #AGGCGGTC   1440                                                                  - - TGCAGCGAGT GGAAGTTCGC CGCCTGTGTG GTGGACCGCC TGTGCCTCAT GG -             #CCTTCTCG   1500                                                                  - - GTCTTCACCA TCATCTGCAC CATCGGCATC CTGATGTCGG CTCCCAACTT CG -             #TGGAGGCC   1560                                                                  - - GTGTCCAAAG ACTTTGCGTA ACCACGCCTG GTTCTGTACA TGTGGAAAAC TC -             #ACAGATGG   1620                                                                  - - GCAAGGCCTT TGGCTTGGCG AGATTTGGGG GTGCTAATCC AGGACAGCAT TA -             #CACGCCAC   1680                                                                  - - AACTCCAGTG TTCCCTTCTG GCTGTCAGTC GTGTTGCTTA CGGTTTCTTT GT -             #TACTTTAG   1740                                                                  - - GTAGTAGAAT CTCAGCACTT TGTTTCATAT TCTCAGATGG GCTGATAGAT AT -             #CCTTGGCA   1800                                                                  - - CATCCGTACC ATCGGTCAGC AGGGCCACTG AGTAGTCATT TTGCCCATTA GC -             #CCACTGCC   1860                                                                  - - TGGAAAGCCC TTCGGA             - #                  - #                       - #  1876                                                                   - -  - - (2) INFORMATION FOR SEQ ID NO:8:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 502 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: unknown                                                 - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                - - Met Arg Cys Ser Pro Gly Gly Val Trp Leu Al - #a Leu Ala Ala Ser Leu       1               5   - #                10  - #                15                - - Leu His Val Ser Leu Gln Gly Glu Phe Gln Ar - #g Lys Leu Tyr Lys Glu                   20      - #            25      - #            30                    - - Leu Val Lys Asn Tyr Asn Pro Leu Glu Arg Pr - #o Val Ala Asn Asp Ser               35          - #        40          - #        45                        - - Gln Pro Leu Thr Val Tyr Phe Ser Leu Ser Le - #u Leu Gln Ile Met Asp           50              - #    55              - #    60                            - - Val Asp Glu Lys Asn Gln Val Leu Thr Thr As - #n Ile Trp Leu Gln Met       65                  - #70                  - #75                  - #80         - - Ser Trp Thr Asp His Tyr Leu Gln Trp Asn Va - #l Ser Glu Tyr Pro Gly                       85  - #                90  - #                95                - - Val Lys Thr Val Arg Phe Pro Asp Gly Gln Il - #e Trp Lys Pro Asp Ile                   100      - #           105      - #           110                   - - Leu Leu Tyr Asn Ser Ala Asp Glu Arg Phe As - #p Ala Thr Phe His Thr               115          - #       120          - #       125                       - - Asn Val Leu Val Asn Ser Ser Gly His Cys Gl - #n Tyr Leu Pro Pro Gly           130              - #   135              - #   140                           - - Ile Phe Lys Ser Ser Cys Tyr Ile Asp Val Ar - #g Trp Phe Pro Phe Asp       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Val Gln His Cys Lys Leu Lys Phe Gly Ser Tr - #p Ser Tyr Gly Gly         Trp                                                                                              165  - #               170  - #               175              - - Ser Leu Asp Leu Gln Met Gln Glu Ala Asp Il - #e Ser Gly Tyr Ile Pro                   180      - #           185      - #           190                   - - Asn Gly Glu Trp Asp Leu Val Gly Ile Pro Gl - #y Lys Arg Ser Glu Arg               195          - #       200          - #       205                       - - Phe Tyr Glu Cys Cys Lys Glu Pro Tyr Pro As - #p Val Thr Phe Thr Val           210              - #   215              - #   220                           - - Thr Met Arg Arg Arg Thr Leu Tyr Tyr Gly Le - #u Asn Leu Leu Ile Pro       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Cys Val Leu Ile Ser Ala Leu Ala Leu Leu Va - #l Phe Leu Leu Pro         Ala                                                                                              245  - #               250  - #               255              - - Asp Ser Gly Glu Lys Ile Ser Leu Gly Ile Th - #r Val Leu Leu Ser Leu                   260      - #           265      - #           270                   - - Thr Val Phe Met Leu Leu Val Ala Glu Ile Me - #t Pro Ala Thr Ser Asp               275          - #       280          - #       285                       - - Ser Val Pro Leu Ile Ala Gln Tyr Phe Ala Se - #r Thr Met Ile Ile Val           290              - #   295              - #   300                           - - Gly Leu Ser Val Val Val Thr Val Ile Val Le - #u Gln Tyr His His His       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Asp Pro Asp Gly Gly Lys Met Pro Lys Trp Th - #r Arg Val Ile Leu         Leu                                                                                              325  - #               330  - #               335              - - Asn Trp Cys Ala Trp Phe Leu Arg Met Lys Ar - #g Pro Gly Glu Asp Lys                   340      - #           345      - #           350                   - - Val Arg Pro Ala Cys Gln His Lys Gln Arg Ar - #g Cys Ser Leu Ala Ser               355          - #       360          - #       365                       - - Val Glu Met Ser Ala Val Ala Pro Pro Pro Al - #a Ser Asn Gly Asn Leu           370              - #   375              - #   380                           - - Leu Tyr Ile Gly Phe Arg Gly Leu Asp Gly Va - #l His Cys Val Pro Thr       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Pro Asp Ser Gly Val Val Cys Gly Arg Met Al - #a Cys Ser Pro Thr         His                                                                                              405  - #               410  - #               415              - - Asp Glu His Leu Leu His Gly Gly Gln Pro Pr - #o Glu Gly Asp Pro Asp                   420      - #           425      - #           430                   - - Leu Ala Lys Ile Leu Glu Glu Val Arg Tyr Il - #e Ala Asn Arg Phe Arg               435          - #       440          - #       445                       - - Cys Gln Asp Glu Ser Glu Ala Val Cys Ser Gl - #u Trp Lys Phe Ala Ala           450              - #   455              - #   460                           - - Cys Val Val Asp Arg Leu Cys Leu Met Ala Ph - #e Ser Val Phe Thr Ile       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Ile Cys Thr Ile Gly Ile Leu Met Ser Ala Pr - #o Asn Phe Val Glu         Ala                                                                                              485  - #               490  - #               495              - - Val Ser Lys Asp Phe Ala                                                               500                                                                 - -  - - (2) INFORMATION FOR SEQ ID NO:9:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 2450 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: both                                                         (D) TOPOLOGY: both                                                    - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 267..1775                                               - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:                                - - GGCTCCTCCC CCTCACCGTC CCAATTGTAT TCCCTGGAAG AGCAGCCGGA AA -              #AGCCTCCG     60                                                                  - - CCTGCTCATA CCAGGATAGG CAAGAAGCTG GTTTCTCCTC GCAGCCAACT CC -             #CTGAGACC    120                                                                  - - CAGGAACCAC CGCGGCGGCC GGCACCACCT GGACCCAGCT CCAGGCGGGC GC -             #GGCTTCAG    180                                                                  - - CACCACGGAC AGCGCCCCAC CCGCGGCCCT CCCCCCGGCG GCGCGCTCCA GC -             #CGGTGTAG    240                                                                  - - GCGAGGCAGC GAGCTATGCC CGCGGC ATG GCC CGG CGC TGC - #GGC CCC GTG         GCG     293                                                                                        - #           Met Ala Arg Arg - #Cys Gly Pro Val Ala                          - #             1     - #          5                          - - CTG CTC CTT GGC TTC GGC CTC CTC CGG CTG TG - #C TCA GGG GTG TGG GGT           341                                                                        Leu Leu Leu Gly Phe Gly Leu Leu Arg Leu Cy - #s Ser Gly Val Trp Gly             10                 - # 15                 - # 20                 - # 25        - - ACG GAT ACA GAG GAG CGG CTG GTG GAG CAT CT - #C CTG GAT CCT TCC CGC           389                                                                        Thr Asp Thr Glu Glu Arg Leu Val Glu His Le - #u Leu Asp Pro Ser Arg                             30 - #                 35 - #                 40               - - TAC AAC AAG CTT ATC CGC CCA GCC ACC AAT GG - #C TCT GAG CTG GTG ACA           437                                                                        Tyr Asn Lys Leu Ile Arg Pro Ala Thr Asn Gl - #y Ser Glu Leu Val Thr                         45     - #             50     - #             55                   - - GTA CAG CTT ATG GTG TCA CTG GCC CAG CTC AT - #C AGT GTG CAT GAG CGG           485                                                                        Val Gln Leu Met Val Ser Leu Ala Gln Leu Il - #e Ser Val His Glu Arg                     60         - #         65         - #         70                       - - GAG CAG ATC ATG ACC ACC AAT GTC TGG CTG AC - #C CAG GAG TGG GAA GAT           533                                                                        Glu Gln Ile Met Thr Thr Asn Val Trp Leu Th - #r Gln Glu Trp Glu Asp                 75             - #     80             - #     85                           - - TAT CGC CTC ACC TGG AAG CCT GAA GAG TTT GA - #C AAC ATG AAG AAA GTT           581                                                                        Tyr Arg Leu Thr Trp Lys Pro Glu Glu Phe As - #p Asn Met Lys Lys Val             90                 - # 95                 - #100                 - #105        - - CGG CTC CCT TCC AAA CAC ATC TGG CTC CCA GA - #T GTG GTC CTG TAC AAC           629                                                                        Arg Leu Pro Ser Lys His Ile Trp Leu Pro As - #p Val Val Leu Tyr Asn                            110  - #               115  - #               120               - - AAT GCT GAC GGC ATG TAC GAG GTG TCC TTC TA - #T TCC AAT GCC GTG GTC           677                                                                        Asn Ala Asp Gly Met Tyr Glu Val Ser Phe Ty - #r Ser Asn Ala Val Val                        125      - #           130      - #           135                   - - TCC TAT GAT GGC AGC ATC TTC TGG CTG CCG CC - #T GCC ATC TAC AAG AGC           725                                                                        Ser Tyr Asp Gly Ser Ile Phe Trp Leu Pro Pr - #o Ala Ile Tyr Lys Ser                    140          - #       145          - #       150                       - - GCA TGC AAG ATT GAA GTA AAG CAC TTC CCA TT - #T GAC CAG CAG AAC TGC           773                                                                        Ala Cys Lys Ile Glu Val Lys His Phe Pro Ph - #e Asp Gln Gln Asn Cys                155              - #   160              - #   165                           - - ACC ATG AAG TTC CGT TCG TGG ACC TAC GAC CG - #C ACA GAG ATC GAC TTG           821                                                                        Thr Met Lys Phe Arg Ser Trp Thr Tyr Asp Ar - #g Thr Glu Ile Asp Leu            170                 1 - #75                 1 - #80                 1 -       #85                                                                               - - GTG CTG AAG AGT GAG GTG GCC AGC CTG GAC GA - #C TTC ACA CCT AGT         GGT      869                                                                     Val Leu Lys Ser Glu Val Ala Ser Leu Asp As - #p Phe Thr Pro Ser Gly                           190  - #               195  - #               200               - - GAG TGG GAC ATC GTG GCG CTG CCG GGC CGG CG - #C AAC GAG AAC CCC GAC           917                                                                        Glu Trp Asp Ile Val Ala Leu Pro Gly Arg Ar - #g Asn Glu Asn Pro Asp                        205      - #           210      - #           215                   - - GAC TCT ACG TAC GTG GAC ATC ACG TAT GAC TT - #C ATC ATT CGC CGC AAG           965                                                                        Asp Ser Thr Tyr Val Asp Ile Thr Tyr Asp Ph - #e Ile Ile Arg Arg Lys                    220          - #       225          - #       230                       - - CCG CTC TTC TAC ACC ATC AAC CTC ATC ATC CC - #C TGT GTG CTC ATC ACC          1013                                                                        Pro Leu Phe Tyr Thr Ile Asn Leu Ile Ile Pr - #o Cys Val Leu Ile Thr                235              - #   240              - #   245                           - - TCG CTA GCC ATC CTT GTC TTC TAC CTG CCA TC - #C GAC TGT GGC GAG AAG          1061                                                                        Ser Leu Ala Ile Leu Val Phe Tyr Leu Pro Se - #r Asp Cys Gly Glu Lys            250                 2 - #55                 2 - #60                 2 -       #65                                                                               - - ATG ACG TTG TGC ATC TCA GTG CTG CTG GCG CT - #C ACG GTC TTC CTG         CTG     1109                                                                     Met Thr Leu Cys Ile Ser Val Leu Leu Ala Le - #u Thr Val Phe Leu Leu                           270  - #               275  - #               280               - - CTC ATC TCC AAG ATC GTG CCT CCC ACC TCC CT - #C GAC GTG CCG CTC GTC          1157                                                                        Leu Ile Ser Lys Ile Val Pro Pro Thr Ser Le - #u Asp Val Pro Leu Val                        285      - #           290      - #           295                   - - GGC AAG TAC CTC ATG TTC ACC ATG GTG CTT GT - #C ACC TTC TCC ATC GTC          1205                                                                        Gly Lys Tyr Leu Met Phe Thr Met Val Leu Va - #l Thr Phe Ser Ile Val                    300          - #       305          - #       310                       - - ACC AGC GTG TGC GTG CTC AAC GTG CAC CAC CG - #C TCG CCC ACC ACG CAC          1253                                                                        Thr Ser Val Cys Val Leu Asn Val His His Ar - #g Ser Pro Thr Thr His                315              - #   320              - #   325                           - - ACC ATG GCG CCC TGG GTG AAG GTC GTC TTC CT - #G GAG AAG CTG CCC GCG          1301                                                                        Thr Met Ala Pro Trp Val Lys Val Val Phe Le - #u Glu Lys Leu Pro Ala            330                 3 - #35                 3 - #40                 3 -       #45                                                                               - - CTG CTC TTC ATG CAG CAG CCA CGC CAT CAT TG - #C GCC CGT CAG CGC         CTG     1349                                                                     Leu Leu Phe Met Gln Gln Pro Arg His His Cy - #s Ala Arg Gln Arg Leu                           350  - #               355  - #               360               - - CGC CTG CGG CGA CGC CAG CGT GAG CGC GAG GG - #C GCT GGA GCC CTC TTC          1397                                                                        Arg Leu Arg Arg Arg Gln Arg Glu Arg Glu Gl - #y Ala Gly Ala Leu Phe                        365      - #           370      - #           375                   - - TTC CGC GAA GCC CCA GGG GCC GAC TCC TGC AC - #G TGC TTC GTC AAC CGC          1445                                                                        Phe Arg Glu Ala Pro Gly Ala Asp Ser Cys Th - #r Cys Phe Val Asn Arg                    380          - #       385          - #       390                       - - GCG TCG GTG CAG GGG TTG GCC GGG GCC TTC GG - #G GCT GAG CCT GCA CCA          1493                                                                        Ala Ser Val Gln Gly Leu Ala Gly Ala Phe Gl - #y Ala Glu Pro Ala Pro                395              - #   400              - #   405                           - - GTG GCG GGC CCC GGG CGC TCA GGG GAG CCG TG - #T GGC TGT GGC CTC CGG          1541                                                                        Val Ala Gly Pro Gly Arg Ser Gly Glu Pro Cy - #s Gly Cys Gly Leu Arg            410                 4 - #15                 4 - #20                 4 -       #25                                                                               - - GAG GCG GTG GAC GGC GTG CGC TTC ATC GCA GA - #C CAC ATG CGG AGC         GAG     1589                                                                     Glu Ala Val Asp Gly Val Arg Phe Ile Ala As - #p His Met Arg Ser Glu                           430  - #               435  - #               440               - - GAC GAT GAC CAG AGC GTG AGT GAG GAC TGG AA - #G TAC GTC GCC ATG GTG          1637                                                                        Asp Asp Asp Gln Ser Val Ser Glu Asp Trp Ly - #s Tyr Val Ala Met Val                        445      - #           450      - #           455                   - - ATC GAC CGC CTC TTC CTC TGG ATC TTT GTC TT - #T GTC TGT GTC TTT GGC          1685                                                                        Ile Asp Arg Leu Phe Leu Trp Ile Phe Val Ph - #e Val Cys Val Phe Gly                    460          - #       465          - #       470                       - - ACC ATC GGC ATG TTC CTG CAG CCT CTC TTC CA - #G AAC TAC ACC ACC ACC          1733                                                                        Thr Ile Gly Met Phe Leu Gln Pro Leu Phe Gl - #n Asn Tyr Thr Thr Thr                475              - #   480              - #   485                           - - ACC TTC CTC CAC TCA GAC CAC TCA GCC CCC AG - #C TCC AAG TGAGGCCCTT           1782                                                                        Thr Phe Leu His Ser Asp His Ser Ala Pro Se - #r Ser Lys                        490                 4 - #95                 5 - #00                             - - CCTCATCTCC ATGCTCTTTC ACCCTGCCAC CCTCTGCTGC ACAGTAGTGT TG -              #GGTGGAGG   1842                                                                  - - ATGGACGAGT GAGCTACCAG GAAGAGGGGC GCTGCCCCCA CAGATCCATC CT -             #TTTGCTTC   1902                                                                  - - ATCTGGAGTC CCTCCTCCCC CACGCCTCCA TCCACACACA GCAGCTCCAA CC -             #TGGAGGCT   1962                                                                  - - GGACCAACTG CTTTGTTTTG GCTGCTCTCC ATCTCTTGTA CCAGCCCAGG CA -             #ATAGTGTT   2022                                                                  - - GAGGAGGGGA GCAAGGCTGC TAAGTGGAAG ACAGAGATGG CAGAGCCATC CA -             #CCCTGAGG   2082                                                                  - - AGTGACGGGC AAGGGGCCAG GAAGGGGACA GGATTGTCTG CTGCCTCCAA GT -             #CATGGGAG   2142                                                                  - - AAGAGGGGTA TAGGACAAGG GGTGGAAGGG CAGGAGCTCA CACCGCACCG GG -             #CTGGCCTG   2202                                                                  - - ACACAATGGT AGCTCTGAAG GGAGGGGAAG AGAGAGGCCT GGGTGTGACC TG -             #ACACCTGC   2262                                                                  - - CGCTGCTTGA GTGGACAGCA GCTGGACTGG GTGGGCCCCA CAGTGGTCAG CG -             #ATTCCTGC   2322                                                                  - - CAAGTAGGGT TTAGCCGGGC CCCATGGTCA CAGACCCCTG GGGGAGGCTT CC -             #AGCTCAGT   2382                                                                  - - CCCACAGCCC CTTGCTTCTA AGGGATCCAG AGACCTGCTC CAGATCCTCT TT -             #CCCCACTG   2442                                                                  - - AAGAATTC                - #                  - #                        - #        2450                                                                   - -  - - (2) INFORMATION FOR SEQ ID NO:10:                                     - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 502 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:                               - - Met Ala Arg Arg Cys Gly Pro Val Ala Leu Le - #u Leu Gly Phe Gly         Leu                                                                                1               5 - #                 10 - #                 15              - - Leu Arg Leu Cys Ser Gly Val Trp Gly Thr As - #p Thr Glu Glu Arg Leu                    20     - #             25     - #             30                   - - Val Glu His Leu Leu Asp Pro Ser Arg Tyr As - #n Lys Leu Ile Arg Pro                35         - #         40         - #         45                       - - Ala Thr Asn Gly Ser Glu Leu Val Thr Val Gl - #n Leu Met Val Ser Leu            50             - #     55             - #     60                           - - Ala Gln Leu Ile Ser Val His Glu Arg Glu Gl - #n Ile Met Thr Thr Asn        65                 - # 70                 - # 75                 - # 80        - - Val Trp Leu Thr Gln Glu Trp Glu Asp Tyr Ar - #g Leu Thr Trp Lys Pro                        85 - #                 90 - #                 95               - - Glu Glu Phe Asp Asn Met Lys Lys Val Arg Le - #u Pro Ser Lys His Ile                   100      - #           105      - #           110                   - - Trp Leu Pro Asp Val Val Leu Tyr Asn Asn Al - #a Asp Gly Met Tyr Glu               115          - #       120          - #       125                       - - Val Ser Phe Tyr Ser Asn Ala Val Val Ser Ty - #r Asp Gly Ser Ile Phe           130              - #   135              - #   140                           - - Trp Leu Pro Pro Ala Ile Tyr Lys Ser Ala Cy - #s Lys Ile Glu Val Lys       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - His Phe Pro Phe Asp Gln Gln Asn Cys Thr Me - #t Lys Phe Arg Ser         Trp                                                                                              165  - #               170  - #               175              - - Thr Tyr Asp Arg Thr Glu Ile Asp Leu Val Le - #u Lys Ser Glu Val Ala                   180      - #           185      - #           190                   - - Ser Leu Asp Asp Phe Thr Pro Ser Gly Glu Tr - #p Asp Ile Val Ala Leu               195          - #       200          - #       205                       - - Pro Gly Arg Arg Asn Glu Asn Pro Asp Asp Se - #r Thr Tyr Val Asp Ile           210              - #   215              - #   220                           - - Thr Tyr Asp Phe Ile Ile Arg Arg Lys Pro Le - #u Phe Tyr Thr Ile Asn       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Leu Ile Ile Pro Cys Val Leu Ile Thr Ser Le - #u Ala Ile Leu Val         Phe                                                                                              245  - #               250  - #               255              - - Tyr Leu Pro Ser Asp Cys Gly Glu Lys Met Th - #r Leu Cys Ile Ser Val                   260      - #           265      - #           270                   - - Leu Leu Ala Leu Thr Val Phe Leu Leu Leu Il - #e Ser Lys Ile Val Pro               275          - #       280          - #       285                       - - Pro Thr Ser Leu Asp Val Pro Leu Val Gly Ly - #s Tyr Leu Met Phe Thr           290              - #   295              - #   300                           - - Met Val Leu Val Thr Phe Ser Ile Val Thr Se - #r Val Cys Val Leu Asn       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Val His His Arg Ser Pro Thr Thr His Thr Me - #t Ala Pro Trp Val         Lys                                                                                              325  - #               330  - #               335              - - Val Val Phe Leu Glu Lys Leu Pro Ala Leu Le - #u Phe Met Gln Gln Pro                   340      - #           345      - #           350                   - - Arg His His Cys Ala Arg Gln Arg Leu Arg Le - #u Arg Arg Arg Gln Arg               355          - #       360          - #       365                       - - Glu Arg Glu Gly Ala Gly Ala Leu Phe Phe Ar - #g Glu Ala Pro Gly Ala           370              - #   375              - #   380                           - - Asp Ser Cys Thr Cys Phe Val Asn Arg Ala Se - #r Val Gln Gly Leu Ala       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Gly Ala Phe Gly Ala Glu Pro Ala Pro Val Al - #a Gly Pro Gly Arg         Ser                                                                                              405  - #               410  - #               415              - - Gly Glu Pro Cys Gly Cys Gly Leu Arg Glu Al - #a Val Asp Gly Val Arg                   420      - #           425      - #           430                   - - Phe Ile Ala Asp His Met Arg Ser Glu Asp As - #p Asp Gln Ser Val Ser               435          - #       440          - #       445                       - - Glu Asp Trp Lys Tyr Val Ala Met Val Ile As - #p Arg Leu Phe Leu Trp           450              - #   455              - #   460                           - - Ile Phe Val Phe Val Cys Val Phe Gly Thr Il - #e Gly Met Phe Leu Gln       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Pro Leu Phe Gln Asn Tyr Thr Thr Thr Thr Ph - #e Leu His Ser Asp         His                                                                                              485  - #               490  - #               495              - - Ser Ala Pro Ser Ser Lys                                                               500                                                                 - -  - - (2) INFORMATION FOR SEQ ID NO:11:                                     - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1915 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: both                                                         (D) TOPOLOGY: both                                                    - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: CDS                                                              (B) LOCATION: 87..1583                                                - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:11:                               - - CCGGCGCTCA CTCGACCGCG CGGCTCACGG GTGCCCTGTG ACCCCACAGC GG -              #AGCTCGCG     60                                                                  - - GCGGCTGCCA CCCGGCCCCG CCGGCCATGA GGCGCGCGCC TTCCCTGGTC CT -             #TTTCTTCC    120                                                                  - - TGGTCGCCCT TTGCGGGCGC GGGAACTGCC GCGTGGCCAA TGCGGAGGAA AA -             #GCTGATGG    180                                                                  - - ACGACCTTCT GAACAAAACC CGTTACAATA ACCTGATCCG CCCAGCCACC AG -             #CTCCTCAC    240                                                                  - - AGCTCATCTC CATCAAGCTG CAGCTCTCCC TGGCCCAGCT TATCAGCGTG AA -             #TGAGCGAG    300                                                                  - - AGCAGATCAT GACCACCAAT GTCTGGCTGA AACAGGAATG GACTGATTAC CG -             #CCTGACCT    360                                                                  - - GGAACAGCTC CCGCTACGAG GGTGTGAACA TCCTGAGGAT CCCTGCAAAG CG -             #CATCTGGT    420                                                                  - - TGCCTGACAT CGTGCTTTAC AACAACGCCG ACGGGACCTA TGAGGTGTCT GT -             #CTACACCA    480                                                                  - - ACTTGATAGT CCGGTCCAAC GGCAGCGTCC TGTGGCTGCC CCCTGCCATC TA -             #CAAGAGCG    540                                                                  - - CCTGCAAGAT TGAGGTGAAG TACTTTCCCT TCGACCAGCA GAACTGCACC CT -             #CAAGTTCC    600                                                                  - - GCTCCTGGAC CTATGACCAC ACGGAGATAG ACATGGTCCT CATGACGCCC AC -             #AGCCAGCA    660                                                                  - - TGGATGACTT TACTCCCAGT GGTGAGTGGG ACATAGTGGC CCTCCCAGGG AG -             #AAGGACAG    720                                                                  - - TGAACCCACA AGACCCCAGC TACGTGGACG TGACTTACGA CTTCATCATC AA -             #GCGCAAGC    780                                                                  - - CTCTGTTCTA CACCATCAAC CTCATCATCC CCTGCGTGCT CACCACCTTG CT -             #GGCCATCC    840                                                                  - - TCGTCTTCTA CCTGCCATCC GACTGCGGCG AGAAGATGAC ACTGTGCATC TC -             #AGTGCTGC    900                                                                  - - TGGCACTGAC ATTCTTCCTG CTGCTCATCT CCAAGATCGT GCCACCCACC TC -             #CCTCGATG    960                                                                  - - TGCCTCTCAT CGGCAAGTAC CTCATGTTCA CCATGGTGCT GGTCACCTTC TC -             #CATCGYCA   1020                                                                  - - CCAGCGTCTG TGTGCTCAAT GTGCACCACC GCTCGCCCAG CACCCACACC AT -             #GGCACCCT   1080                                                                  - - GGGTCAAGCG CTGCTTCCTG CACAAGCTGC CTACCTTCCT CTTCATGAAG CG -             #CCCTGGCC   1140                                                                  - - CCGACAGCAG CCCGGCCAGA GCCTTCCCGC CCAGCAAGTC ATGCGTGACC AA -             #GCCCGAGG   1200                                                                  - - CCACCGCCAC CTCCACCAGC CCCTCCAACT TCTATGGGAA CTCCATGTAC TT -             #TGTGAACC   1260                                                                  - - CCGCCTCTGC AGCTTCCAAG TCTCCAGCCG GCTCTACCCC GGTGGCTATC CC -             #CAGGGATT   1320                                                                  - - TCTGGCTGCG GYCCTCTGGG AGGTTCCGAC AGGATGTGCA GGAGGCATTA GA -             #AGGTGTCA   1380                                                                  - - GCTTCATCGC CCAGCACATG AAGAATGDCG ATGAAGACCA GAGTGTCGCT GA -             #GGACTGGA   1440                                                                  - - AGAACGTGGC TATGGTGGTG GACCGGCTGT TCCTGTGGGT GTTCATGTTT GT -             #GTGCGTCC   1500                                                                  - - TGGGCTCTGT GGGGCTCTTC CTGCCGCCCC TCTTCCAGAC CCATGCAGCT TC -             #TGAGGGGC   1560                                                                  - - CCTACGCTGC CCAGCGTGAC TGAGGGCCCC CTGGGTTGTG GGGTGAGAGG AT -             #GTGAGTGG   1620                                                                  - - CCGGGTGGGC ACTTTGCTGC TTCTTTCTGG GTTGTGGCCG ATGAGGCCCT AA -             #GTAAATAT   1680                                                                  - - GTGAGCATTG GCCATCAACC CCATCAAACC AGCCACAGCC GTGGAACAGG CA -             #AGGATGGG   1740                                                                  - - GGCCTGGCCT GTCCTCTCTG AATGCCTTGG AGGGATCCCA GGAAGCCCCA GT -             #AGGAGGGA   1800                                                                  - - GCTTCAGACA GTTCAATTCT GGCCTGTCTT CCTTCCCTGC ACCGGGCAAT GG -             #GGATAAAG   1860                                                                  - - ATGACTTCGT AGCAGCACCT ACTATGCTTC AGGCATGGTG CCGGCCTGCC TC - #TCC             1915                                                                        - -  - - (2) INFORMATION FOR SEQ ID NO:12:                                     - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 498 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: unknown                                                 - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12:                               - - Met Arg Arg Ala Pro Ser Leu Val Leu Phe Ph - #e Leu Val Ala Leu Cys       1               5   - #                10  - #                15                - - Gly Arg Gly Asn Cys Arg Val Ala Asn Ala Gl - #u Glu Lys Leu Met Asp                   20      - #            25      - #            30                    - - Asp Leu Leu Asn Lys Thr Arg Tyr Asn Asn Le - #u Ile Arg Pro Ala Thr               35          - #        40          - #        45                        - - Ser Ser Ser Gln Leu Ile Ser Ile Lys Leu Gl - #n Leu Ser Leu Ala Gln           50              - #    55              - #    60                            - - Leu Ile Ser Val Asn Glu Arg Glu Gln Ile Me - #t Thr Thr Asn Val Trp       65                  - #70                  - #75                  - #80         - - Leu Lys Gln Glu Trp Thr Asp Tyr Arg Leu Th - #r Trp Asn Ser Ser Arg                       85  - #                90  - #                95                - - Tyr Glu Gly Val Asn Ile Leu Arg Ile Pro Al - #a Lys Arg Ile Trp Leu                   100      - #           105      - #           110                   - - Pro Asp Ile Val Leu Tyr Asn Asn Ala Asp Gl - #y Thr Tyr Glu Val Ser               115          - #       120          - #       125                       - - Val Tyr Thr Asn Leu Ile Val Arg Ser Asn Gl - #y Ser Val Leu Trp Leu           130              - #   135              - #   140                           - - Pro Pro Ala Ile Tyr Lys Ser Ala Cys Lys Il - #e Glu Val Lys Tyr Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Pro Phe Asp Gln Gln Asn Cys Thr Leu Lys Ph - #e Arg Ser Trp Thr         Tyr                                                                                              165  - #               170  - #               175              - - Asp His Thr Glu Ile Asp Met Val Leu Met Th - #r Pro Thr Ala Ser Met                   180      - #           185      - #           190                   - - Asp Asp Phe Thr Pro Ser Gly Glu Trp Asp Il - #e Val Ala Leu Pro Gly               195          - #       200          - #       205                       - - Arg Arg Thr Val Asn Pro Gln Asp Pro Ser Ty - #r Val Asp Val Thr Tyr           210              - #   215              - #   220                           - - Asp Phe Ile Ile Lys Arg Lys Pro Leu Phe Ty - #r Thr Ile Asn Leu Ile       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Ile Pro Cys Val Leu Thr Thr Leu Leu Ala Il - #e Leu Val Phe Tyr         Leu                                                                                              245  - #               250  - #               255              - - Pro Ser Asp Cys Gly Glu Lys Met Thr Leu Cy - #s Ile Ser Val Leu Leu                   260      - #           265      - #           270                   - - Ala Leu Thr Phe Phe Leu Leu Leu Ile Ser Ly - #s Ile Val Pro Pro Thr               275          - #       280          - #       285                       - - Ser Leu Asp Val Pro Leu Ile Gly Lys Tyr Le - #u Met Phe Thr Met Val           290              - #   295              - #   300                           - - Leu Val Thr Phe Ser Ile Xaa Thr Ser Val Cy - #s Val Leu Asn Val His       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - His Arg Ser Pro Ser Thr His Thr Met Ala Pr - #o Trp Val Lys Arg         Cys                                                                                              325  - #               330  - #               335              - - Phe Leu His Lys Leu Pro Thr Phe Leu Phe Me - #t Lys Arg Pro Gly Pro                   340      - #           345      - #           350                   - - Asp Ser Ser Pro Ala Arg Ala Phe Pro Pro Se - #r Lys Ser Cys Val Thr               355          - #       360          - #       365                       - - Lys Pro Glu Ala Thr Ala Thr Ser Thr Ser Pr - #o Ser Asn Phe Tyr Gly           370              - #   375              - #   380                           - - Asn Ser Met Tyr Phe Val Asn Pro Ala Ser Al - #a Ala Ser Lys Ser Pro       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Ala Gly Ser Thr Pro Val Ala Ile Pro Arg As - #p Phe Trp Leu Arg         Xaa                                                                                              405  - #               410  - #               415              - - Ser Gly Arg Phe Arg Gln Asp Val Gln Glu Al - #a Leu Glu Gly Val Ser                   420      - #           425      - #           430                   - - Phe Ile Ala Gln His Met Lys Asn Xaa Asp Gl - #u Asp Gln Ser Val Ala               435          - #       440          - #       445                       - - Glu Asp Trp Lys Asn Val Ala Met Val Val As - #p Arg Leu Phe Leu Trp           450              - #   455              - #   460                           - - Val Phe Met Phe Val Cys Val Leu Gly Ser Va - #l Gly Leu Phe Leu Pro       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Pro Leu Phe Gln Thr His Ala Ala Ser Glu Gl - #y Pro Tyr Ala Ala         Gln                                                                                              485  - #               490  - #               495              - - Arg Asp                                                                  __________________________________________________________________________ 

That which is claimed:
 1. An isolated nucleic acid molecule, comprising a sequence of nucleotides that encodes an α₄ subunit of a human neuronal nicotinic acetylcholine receptor, wherein the sequence of nucleotides or ribonucleotides encoding the α₄ subunit is selected from the group consisting of:(a) a sequence of nucleotides or ribonucleotides that encodes a human α₄ subunit and comprises the coding portion of the sequence set forth in SEQ ID No. 5; (b) a sequence of nucleotides or ribonucleotides that encodes a human α₄ subunit and that hybridizes under conditions of high stringency to the complement of the entire coding portion of the sequence of nucleotides set forth in SEQ ID No. 5; (c) a sequence of nucleotides that encodes an α₄ subunit, hybridizes under conditions of high stringency to the sequence of nucleotides set forth in SEQ ID No. 5, and, if it is DNA, is fully complementary or, if it is RNA, is identical to mRNA native to a human cell; and (d) a sequence of nucleotides or ribonucleotides degenerate with the α₄ subunit-encoding sequence of (a), (b) or (c).
 2. An isolated nucleic acid molecule, encoding an α₄ subunit of a human neuronal nicotinic acetylcholine receptor, wherein the α₄ subunit comprises the sequence of amino acids set forth in SEQ ID No.
 6. 3. An isolated nucleic acid molecule that encodes an α₄ subunit of a human neuronal nicotinic acetylcholine receptor, wherein the α₄ subunit comprises:the sequence of amino acids encoded by clone HnAChRα4.2 deposited under ATCC Accession No. 69239, or the sequence of amino acids encoded by clone HnAChRα4.1 deposited under ATCC Accession No.
 69152. 4. An isolated nucleic acid molecule that encodes a human neuronal nicotinic acetylcholine receptor α₄ subunit that hybridizes under high stringency conditions:to the complement of the entire coding sequence set forth in SEQ ID No:5 or to the complement of the entire sequence of the α₄ -encoding insert of clone HnAChRα4.2 deposited under ATCC Accession No. 69239, or to the complement of the α₄ -encoding insert of clone HnAChRα4.1 deposited under ATCC Accession No.
 69152. 5. The nucleic acid molecule of claim 1, wherein said nucleic acid molecule is selected from the group consisting of molecules that:(i) comprise the sequence of nucleotides set forth as nucleotides 173-2056 in SEQ ID No:5 or ribonucleotides encoded by SEQ ID No. 5, or (ii) comprise the α₄ -encoding insert of clone HnAChRα4.2 deposited under ATCC Accession No. 69239 or ribonucleotides encoded by the insert, or (iii) comprise the α₄ -encoding insert of clone HnAChRα4.1 deposited under ATCC Accession No. 69152 or ribonucleotides encoded by the insert.
 6. Isolated cells, comprising the nucleic acid molecule of claim 1, wherein said cells are bacterial cells, mammalian cells or amphibian oocytes, and the nucleic acid molecule is heterologous to the cells.
 7. The cells of claim 6, further containing a nucleic acid molecule encoding a β subunit of human neuronal nicotinic acetylcholine receptor.
 8. The cells of claim 7, wherein said β subunit is selected from β₂ or β₄.
 9. The cells of claim 7, wherein said β subunit is β₄.
 10. The cells of claim 6, wherein:said cells express functional neuronal nicotinic acetylcholine receptors that contain one or more subunits encoded by said nucleic acid molecule; and the cells are eukaryotic cells.
 11. An isolated human neuronal nicotinic acetylcholine receptor, comprising an α₄ subunit encoded by the nucleic acid molecule of claim
 1. 12. An isolated human neuronal nicotinic acetylcholine receptor subunit, comprising an α₄ subunit encoded by the nucleic acid of claim
 1. 13. The isolated human neuronal nicotinic acetylcholine receptor of claim 11, further comprising at least one human neuronal nicotinic acetylcholine receptor beta subunit.
 14. The nucleic acid molecule of claim 1, wherein said nucleic acid molecule is mRNA.
 15. Isolated mammalian and amphibian cells containing the mRNA of claim
 14. 16. The cells of claim 15, wherein said cells further contain mRNA encoding a beta subunit of a human neuronal nicotinic acetylcholine receptor.
 17. The nucleic acid molecule of claim 1, comprising the sequence of nucleotides set forth as nucleotides 173-2056 in SEQ ID No.
 5. 18. The nucleic acid molecule of claim 1, comprising the sequence of nucleotides set forth in SEQ ID No.
 5. 19. The cells of claim 6, wherein said cells express neuronal nicotinic acetylcholine receptors.
 20. The cells of claim 7, wherein said cells express neuronal nicotinic acetylcholine receptors.
 21. The nucleic acid molecule of claim 1, wherein the nucleic acid molecule is fully complementary to or identical to DNA isolated from or present in a human DNA library.
 22. The mammalian cells and amphibian cells of claim 16, wherein said cells express functional neuronal nicotinic acetylcholine receptors that contain one or more subunits encoded by said isolated nucleic acid molecule.
 23. The nucleic acid molecule of claim 1 that is DNA.
 24. A clone having all of the identifying characteristics of clone HnAChRα4.1 deposited under ATCC Accession No.
 69152. 25. A clone having all of the identifying characteristics of clone HnAChRα4.2 deposited under ATCC Accession No.
 69239. 26. A method for identifying functional neuronal nicotinic acetylcholine receptor subunits and combinations thereof, said method comprising:(a) introducing the nucleic acid molecule of claim 1 and optionally a nucleic acid molecule encoding at least one beta subunit of a human neuronal nicotinic acetylcholine receptor into mammalian or amphibian cells; and (b) assaying for neuronal nicotinic acetylcholine receptor activity in cells of step (a). 